Genetic control of cell size

ABSTRACT

Described herein are mutant cyanobacterial cell populations that have a smaller mean cell length than wild type cyanobacterial cell populations of the same species.

This application claims benefit of priority to the filing date of U.S.Provisional Application Ser. No. 62/377,964, filed Aug. 22, 2016, thecontents of which are specifically incorporated herein by reference intheir entity.

FEDERAL FUNDING

This invention was made with government support under MCB1517241 awardedby the National Science Foundation. The government has certain rights inthe invention.

BACKGROUND OF THE INVENTION

Despite the importance of cyanobacteria as the base of many ecologicalsystems, their biotechnological applications, and their evolutionaryrelationship to plant and algal chloroplasts, molecular mechanisms ofcyanobacterial division have remained largely unstudied. Whilecyanobacteria may share some division factors with other bacteria,several unique cyanobacterial features, including thylakoid membranes,multiple chromosome copies, and lack of nucleoid occlusion, distinguishthem from classic prokaryotic model organisms and complicateextrapolation of their division mechanisms.

Cyanobacteria have been employed for the production of sustainablebiofuels, pharmaceuticals, and chemicals due to their: (i)photosynthetic efficiency; (ii) low nutrient requirements; (iii)capacity to grow on non-arable landmass and with water supplies unfitfor traditional agriculture; and (iv) ease of genetic manipulation.Despite the advantages of cyanobacteria, current practices for thecultivation, harvesting, and processing of cyanobacterial “crops” areexpensive and infrastructure-intensive. These costs represent asignificant economic barrier to cyanobacterial bioproduction, regardlessof the specific target product. While research efforts have placed focuson improving photosynthetic efficiency or metabolic engineering in orderto achieve higher total yields, there has been little progress onengineering cyanobacteria in order to relieve theseharvesting/processing costs that currently prohibit widespread adoption.

SUMMARY

New strains of cyanobacteria and bacteria are described herein withmodifications to the genes/proteins that provide control over cellulardivision and cellular morphology. The methods and new strains are usefulfor improving cyanobacterial/bacterial harvest and cellular lysis.

Cyanobacteria and other types of bacteria are emerging as alternativecrop species for the production of fuels, chemicals, and biomass. Yet,the success of these microbes depends upon the development ofcost-effective technologies that permit scaled cultivation and cellharvesting.

Three of the most significant costs associated with cyanobacterialcultivation are related to mixing cultures, recovering and dewateringcell biomass, and lysis of cyanobacterial cells to obtain intracellularmetabolites. These processes can account for up to 40% of operatingcosts. There are intrinsic properties of cyanobacterial cells that caninfluence the costs associated with each of these processes, but optimalcyanobacteria properties vary with the stage of cultivation. Forexample, during growth of a culture, cyanobacterial cells are ideallybuoyant and small so that the mixing costs required to keep them insuspension are minimized. Yet, small, buoyant cells are difficult toharvest, typically requiring centrifugation or filtration processeswhere the volume of liquid that to be handled can be large. Therefore,at the harvesting stage an ideal cyanobacterium would be large, anddense relative to most wild type cyanobacteria cells. Such large cellsizes facilitate accumulation of useful products within the cell andallow for spontaneous (gravity) precipitation from solution duringharvest, thereby increasing product yield and reducing energyexpenditure required to recover cell mass. Finally, processingcyanobacterial cell mass can involve lysing the cells to recoverinternal products. An ideal cyanobacterium would be readily lysed bystandard procedures following harvest, but would not be sickly or havean otherwise compromised cell wall while being actively grown.

As illustrated herein, altered expression of several types of genes canlead to cell elongation through disruption of FtsZ assembly and celldivision. FtsZ is a cytoskeletal polymer that is needed forestablishment of the divisome and the regulation of cell division. TheMin system regulates FtsZ assembly and positioning. MinC and Cdv3 aretwo proteins that are components of the cyanobacterial Min system.Cyanobacterial strains overexpressing MinC, MinD, cdv3, or Ftn2 exhibitdelayed/impaired divisome formation and therefore continue to rapidlygrow but do not divide, becoming elongated relative to unmodifiedstrains. Cyanobacterial cells that overexpress MinC, MinD, cdv3, or Ftn2can have cell sizes that are 2-fold to 20000-fold larger than unmodifiedwild type strains. Hyper-elongated cells exhibit increased rates ofsedimentation under low centrifugal forces or by gravity-assistedsettling. Furthermore, hyper-elongated cells are also more susceptibleto lysis through the application of mild physical strain.

Altering the activity of other FtsZ-regulatory genes such as MinE orMinD can also alter the morphology and length of cyanobacterial cells.Overexpression of MinE decreases cell size. Overexpression of MinDgenerates a distribution of both large and small cells.

Methods are described herein that allow cyanobacterial cell size to betuned and controlled so that the sedimentation rate, susceptibility tocell lysis, and resistance to sheer forces of the cells are ideallysuited for growth, harvesting, and recovery of commercially usefulcomponents from the cells. In some embodiments, expression of MinCprotein, MinD protein, MinE protein, Cdv3 (DivIVA) protein, FtsZprotein, Ftn2 protein, or a combination thereof in a cyanobacteria isfrom a heterologous promoter. In some cases, one or more native genesencoding one or more MinC protein, MinD protein, MinE protein, Cdv3(DivIVA) protein, FtsZ protein, or Ftn2 protein can be mutated ordeleted. Such mutant cells can be smaller than wild type cells.

In some cases, one or more native genes encoding one or more MinCprotein, MinD protein, MinE protein, Cdv3 (DivIVA) protein, FtsZprotein, or Ftn2 protein can be mutated or deleted so that expression ofMinC protein, MinD protein, MinE protein, Cdv3 (DivIVA) protein, FtsZprotein, Ftn2 protein, or a combination is from the heterologouspromoter. The average size of cells in the population can be modulatedby turning on or off such an inducible promoter.

New strains of cyanobacteria are described herein where the cell sizecan be modulated to facilitate growth, harvesting of cells, andprocessing of products made by the cells.

DESCRIPTION OF THE FIGURES

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1A-1G illustrates Cyanobacterial Min Homologs. FIG. 1Aschematically illustrates established Bacillus subtilis and Escherichiacoli Min system models (Lukenhaus, Annu Rev Biochem 76:539-62 (2007);Eswaramoorthy et al., mBio 2: e00257-11 (2011)). FIG. 1B illustrates theoperon organization and genomic context of MinC, MinD, and MinE in S.elongatus. FIG. 1C illustrates some of the structural features of S.elongatus (Se) MinC that are conserved compared to the E. coli (Ec)and/or B. subtilis (Bs) MinC (SEQ ID NOs: 105-107). FIG. 1D illustratessome of the structural features of S. elongatus (Se) MinD that areconserved compared to the E. coli (Ec) and/or B. subtilis (Bs) MinD (SEQID NOs: 108-110). FIG. 1E illustrates some of the structural features ofS. elongatus (Se) MinE that are conserved compared to the E. coli (Ec)and/or B. subtilis (Bs) MinE (SEQ ID NOs: 111-112). Red bars above thealignments show the positions of the indicated α-helices, includingmembrane targeting sequences (MTS) and MinE contact helix, in the E.coli proteins. Red letter sequences indicate equivalent predictedstructures in B. subtilis and S. elongatus homologs. Blue in FIG. 1Eshows that the β1 sheet within the E. coli MinE contact helix is alsopredicted in S. elongatus MinE. FIG. 1F is a schematic illustration ofconstruct designs. In S. elongatus, MinC and DivIVA are expressedindividually, whereas MinD and MinE are in the same operon with aputative ferredoxin-like gene (blue) of unknown function. In mNG-MinC,MinC was codon-optimized (CO) to increase transformation frequency. FIG.1G shows PCR verification of Min gene deletions.

FIG. 2A-2G illustrate the effects of cyanobacterial Min Homologs oncell-size and FtsZ positioning. FIG. 2A shows histograms of S. elongatuscell sizes measured in deletion (green) or overexpression (blue) strainsof MinC, MinD, and MinE relative to the wild type (WT; red) distribution(n=1000 cells per condition). Mean±standard deviation reported inparentheses for each strain. FIG. 2B illustrates that FtsZ (white)localization is altered in Min deletion (Δ) or overexpression (OE) celllines as visualized by immunofluorescence. Chlorophyll a fluorescence isshown in red; Z rings are shown by yellow arrowheads; FtsZ helicalfilaments are shown by blue arrowheads. Scale bars 5 μm. FIG. 2C showsadditional wide-field images of MinCDE and Cdv3 deletion andoverexpression strains stained with anti-FtsZ. Chlorophyll fluorescenceshown in red; FtsZ staining in white. FIG. 2D illustrates the extremecell filamentation in Cdv3 overexpression strains. FIG. 2E illustratesthe quantity of MinC expression as induced by increasing concentrationsof theophylline. FIG. 2F illustrates the quantity of Cdv3 expression asinduced by increasing concentrations of theophylline. FIG. 2Ggraphically illustrates the cyanobacterial growth rate in response toincreasing theophylline inducer. Wild-type S. elongatus was incubatedwith increasing concentrations of theophylline and monitored for growthover 24 hours by optical density at 750 nm (OD₇₅₀). Doubling time wascalculated for n≥4 independent day experiments. Error bars representstandard deviation and the p value for the only significant (p<0.05)change in doubling time is denoted, as determined from pairwise unequalvariances t-tests.

FIG. 3A-3I illustrate construct designs and expression patterns of MinCand MinD in various genetic backgrounds. FIG. 3A schematicallyillustrates constructs where mNG-MinC (mNG, light green) fusions areexpressed from the MinC promoter (P, yellow) but a specR replacement ofthe S. elongatus MinC coding region eliminates MinC expression (ΔminC).The segment encoding the MinC fusion partner was codon-optimized (CO) toincrease transformation frequency. When mNG-MinC was expressed fromNeutral Site 2 (NS2), a 5′ synthetic riboswitch (RS, brown) was operablylinked to control translation. FIG. 3B illustrates that native MinD(red) and native MinE (dark green) coding regions are in the same operonalong with a putative ferredoxin-like gene (orange) of unknown function.Replacement of the S. elongatus MinD (ΔminD) or MinE (ΔminE) codingregion eliminates MinD or MinE expression. Moreover, ΔminD and ΔminEdeletion strains were codon optimized (CO) to increase transformationfrequency. Also shown is a mNG-MinD fusion construct. Native homologyregions of around 1000 bp (purple) were used to fully replace at thenative loci, whereas homology regions (bright blue) were used to insertat NS2. FIG. 3C also illustrates that native cdv3 is expressed from itsown promoter (P, yellow) and that cdv3 is clustered with coaD (darkblue), a component of Co-enzyme A synthesis. Generation of deletionstrains were performed by full replacement of the native gene (SpecR,grey) with a selectable marker, whereas fluorescent and overproductionstrains had a selectable marker positioned as to not interfere withexpression (KanR, grey). FIG. 3D graphically illustrates that theperiodicity of mNG-MinC increases proportionally with cell length (n=10cells per cell length). FIG. 3E illustrates time lapse imaging of thepole-to-pole oscillations of mNG-MinC and mNG-MinD when expressed from asynthetic riboswitch, as compared to natively-expressed mNG-MinC, whichexhibits similar pole-to-pole oscillations. White dots indicate cellperimeters. Images taken every 30 seconds. Scale bar 1 μm. FIG. 3Fillustrates that in ΔminD backgrounds, the native mNG-MinC signal isdiffuse, not recruited to the membrane or midcell. Also the mNG-MinCsignal does not oscillate. FIG. 3G illustrates that mNG-MinC exhibits aneven distribution pattern in ΔminD background, exhibiting a loss ofpole-to-pole oscillation and membrane recruitment. FIG. 3H illustratesthat in ΔminE strains, the natively expressed mNG-MinC formed helicalpatterns along the membrane (red arrowheads) and intermittent ring-likestructures (blue arrowheads). FIG. 3I illustrates that mNG-MinClocalization is disrupted in strains with an incomplete minE knockout.Oscillation of mNG-MinC is lost and helix-like patterning forms alongthe membrane.

FIG. 4A-4I illustrate that Cdv3 is involved in recruiting asubpopulation of MinC to the midcell. FIG. 4A illustrates the operonstructure and genomic context of cdv3 in S. elongatus. The percentprimary sequence identity of Cdv3 in S. elongatus is shown below thediagram in comparison to DivIVA of B. subtilis. Scale bar, 500 bp. FIG.4B illustrates the secondary structure of B. subtilis DivIVA incomparison to S. elongatus Cdv3. Both proteins are predicted to consistlargely of α-helices (red), which comprise the coiled-coil structuresspanning the length of DivIVA. Delta-Blast identified a putative partialB. subtilis DivIVA domain (MPLTPNDIHNKTFTKSFRGYDE-DEVNEFLAQVRKDY; SEQ IDNO:1) in S. elongatus Cdv3 (LDGTRVPLSGRILVRENDLLDLLDD VRAFLPAAIQQA; SEQID NO:2). Within the crossed loop region required for DivIVA binding tonegatively curved membranes (bottom of FIG. 4B; green), Cdv3 lacksconservation of key residues and secondary structure features. FIG. 4Cillustrates that natively-expressed Cdv3-mNG concentrates into aring-like structure at midcell in S. elongatus. Scale bar 5 μm. FIG. 4Dillustrates the midcell localization of mNG-MinC is lost in the absenceof Cdv3. Scale bar 5 μm. FIG. 4E shows histograms illustrating thatdeletion (green) of cdv3 influences the length of S. elongatus cells(n=1000) compared to wild type cells. The mean cell length of Δcdv3cells was 4.54±1.41 (standard deviation) as shown in parentheses. FIG.4F illustrates that FtsZ (white) localization is altered in Δcdv3 orcdv3 overexpression (OE) cyanobacterial lines as visualized byimmunofluorescence with α-FtsZ antibodies. Chlorophyll a fluorescence,red; Z rings, yellow arrowheads; FtsZ helical filaments, bluearrowheads. Scale bars 10 μm. FIG. 4G illustrates that in the absence ofcdv3, mNG-MinC oscillations are apparent. However, in elongated cellsmultiple mNG-MinC wave patterns are observed instead of pole-to-poleoscillations (blue arrowheads). The mid-cell localization of mNG-MinC islost in both ΔminD and Δcdv3 strains. FIG. 4H illustrates that DivIVA(also called cdv3 in S. elongatus) localization to division planes isindependent of other Min system regulators. DivIVA-mNG was imaged inΔminC, ΔminD and ΔminE backgrounds. Upon the deletion of minC, theDivIVA signal appeared at midcell. Likewise, in ΔminD backgrounds,DivIVA localization appeared in ring-like patterns that were oftenobserved in multiple locations and which were frequently near cellpoles. These localizations are consistent with FtsZ staining in ΔminCand ΔminD cells, respectively. Interestingly, ΔminE cells displayederratic DivIVA-mNG localization, where ring-like structures formedrandomly in the cell (often at constricting sites presumed to bedivision planes), while also forming a helical pattern that wasreminiscent of FtsZ patterning in ΔminE cells. These patterns allindicate co-localization of DivIVA and FtsZ in S. elongatus. FIG. 4Ishows images of cyanobacterial cells illustrating immunolocalization ofFtsZ (yellow) in representative cells with Cdv3 expression induced forthe indicated number of hours. Formation of Z-rings was delayed inCdv3-mTurq (blue) expressing lines (24 hr-OE) while multiple,mispositioned Z-rings are evident in highly elongated cells (48-72 hourspost-induction) without clear indications of constriction. Scale barsfor (C)=10 μm.

FIG. 5A-5F illustrate cyanobacterial cell elongation when MinC, MinD,MinE, and/or Cdv3 proteins are overexpressed. FIG. 5A is a schematicdiagram of a cyanobacterial cell illustrating the locations of MinC,MinD, MinE, Cdv3, and FtsZ proteins, as well as the effect ofoverexpressing MinC protein on cell length. FIG. 5B graphicallyillustrates cell length upon inducing expression of MinC protein (leftpanel) and MinD protein (right panel) with increased amounts of theexpression inducer (theophylline). As illustrated, greaterconcentrations of the theophylline inducer led to cyanobacterialpopulations with increased mean cell lengths. FIG. 5C graphicallyillustrates cell length upon inducing expression of MinE protein (leftpanel) and Cdv3 protein (right panel) with increased amounts of theexpression inducer (theophylline). As illustrated, greaterconcentrations of the theophylline inducer led to cyanobacterialpopulations with increased mean cell lengths. FIG. 5D graphicallyillustrates cell length upon inducing expression of MinD protein (leftpanel) with varying amounts of the inducer (theophylline), and images ofcells after 96 hours of MinD protein induction by 2 mM theophylline(right panel). As illustrated, greater concentrations of thetheophylline inducer lead to cyanobacterial populations with increasedmean cell lengths. FIG. 5E graphically illustrates cell length atvarious times after inducing expression of MinE protein (left panel) andCdv3 protein (right panel) with varying amounts of the inducer(theophylline). As illustrated, greater concentrations of thetheophylline inducer lead to cyanobacterial populations with increasedmean cell lengths. FIG. 5F shows brightfield microscopy images ofelongated cyanobacterial cells that have been induced to over-expressCdv3. The scale of these images was changed between panels to capturethe extreme elongation that is seen in these cells.

FIG. 6A-6C illustrate enhanced sedimentation of hyper-elongated cellsthat overexpress Cdv3 (DivIVA). FIG. 6A illustrates sedimentation ofhyper-elongated cells that overexpress Cdv3 (DivIVA) in a graduatedcylinder at 0 hours and 24 hours of sedimentation without application ofadditional gravitational forces. FIG. 6B also illustrates sedimentationof hyper-elongated cells that overexpress Cdv3 (DivIVA at 0 hours and 24hours of sedimentation without application of additional gravitationalforces. FIG. 6C graphically illustrates sedimentation of hyper-elongatedcells that overexpress Cdv3 (DivIVA compared to cells that overexpressMinE when additional gravitational forces were applied.

FIG. 7A-7E illustrates that hyper-elongated cells that overexpress Cdv3(DivIVA) are more readily lysed by torsional/shear forces than controlcells that do not overexpress Cdv3 (DivIVA). FIG. 7A illustrates themorphological changes that occur following overexpression of Cdv3 by theaddition of theophylline, as reflected by changes in the lightscattering and fluorescent properties of cells when analyzed by flowcytometry. Cdv-3 overexpression (Cdv3-OE) strains were analyzed by flowcytometry a 0 hours (top), 24 hours (middle), or 48 hours (bottom) afterinduction of Cdv-3 expression by addition of theophylline. An increasein the forward scatter and chlorophyll-associated red autofluorescencewas observed that is correlated with the increased cell size ofCdv3-overexpressing cells. Cell counts are gated into wild type-length(blue box) and elongated (red box) to facilitate quantification. FIG. 7Bshows representative experiments to illustrate the effects of increasingpressure and lytic forces from a cell disrupter when applied to bothuninduced (top) and Cdv3-overexpressing (bottom) cyanobacterialcultures, as measured by flow cytometry. The proportion of elongatedcells (red) relative to WT lengths (blue) is represented in pie chartsfor each condition. The application of even very mild sheer forceresults in preferential lysis of the hyperelongated cell population.FIG. 7C graphically illustrates the proportion of intact cells remainingfollowing cell disruption with increasing pressures, as shown in 7B.FIG. 7D graphically illustrates the proportion of intact cells remainingfollowing cell disruption as in FIG. 7C, but where only the proportionof elongated cells is tracked. FIG. 7E graphically illustrates dry cellweight of harvested control (uninduced, dark grey) andCdv3-overexpressing (induced, light grey) cyanobacterial cells, showingthat Cdv3 overexpression does not adversely affect cell biomassaccumulation or recovery of biomass from harvesting. The p valuesdisplayed are from unequal variances t-tests with n=4 biologicalreplicates.

FIG. 8 illustrates cyanobacterial cell elongation when Ftn2 isoverexpressed from an IPTG-inducible promoter. Representativecyanobacterial cells (red: chlorophyll fluorescence) are elongatedrelative to wildtype cells. Additionally, this image illustrates thatFtsZ (white) localization is altered in Ftn2 overexpression (OE)cyanobacterial lines, as visualized by immunofluorescence with anti-FtsZantibodies.

DETAILED DESCRIPTION

While cyanobacteria and algae can offer many benefits relative totraditional land plants for production of commercially useful products,commercialization of photosynthetic crop species has been limited due totechnical problems relating to scaled cultivation. Cyanobacteria exhibitrapid division times, high photosynthetic efficiencies, the capacity tobe cultivated in non-potable water supplies on non-arable lands. Inaddition, cyanobacteria are readily genetically manipulated. Thesefeatures that make them of considerable interest as alternative cropspecies. Yet, these advantages are overshadowed by several economicconsiderations that have stymied widespread cultivation of alternativemicroalgal crops. In contrast to the technology for plants that has beenunder development for millennia, the infrastructure, strains andequipment for cyanobacterial crops are still emerging.

One of the largest economic obstacles to cyanobacterial biotechnology isrelated to the costs of harvesting and processing cells for the recoveryof biomass. Three of the most significant costs associated withcyanobacterial cultivation are related to mixing cultures, recoveringand dewatering cell biomass, and lysis of cyanobacterial cells to obtainintracellular metabolites (accounting for up to ˜40% of operatingcosts). Although the industry has attempted several procedures toovercome these problems (e.g., chemical flocculants, mechanicalseparation by filtration or centrifugation, etc.) such procedures can beexpensive, for example, because they may introduce chemicals that needto be removed later and cannot be recycled, or because expensiveequipment is required to isolate the cells.

As illustrated herein, the size or length of cyanobacterial cells can beregulated by modulating the expression of minC, minD, minE, cdv3 (alsocalled DivIVA), FtsZ, Ftn2, or combinations thereof. In wild-type (WT)cyanobacterial cells, cell sizes are within a narrow range of about1.7-4.5 μm (mean cell length 3.10±0.66 μm; FIG. 2A-2B). However, bymodulating the expression of Min genes (or transgenes), the sizes ofcells can be significantly altered.

For example, the Min proteins can interact with and modulate thecapacity of FtsZ to assemble into the filaments that make up the ringsthat ultimately divide the cell. Reduced expression and/or activity ofat least one of minC, or minD generally produces cyanobacterialpopulations containing small cells. However, reduce expression of FtsZcan produce elongated cells. Overexpression (OE) of minC, minD, minE,cdv3 (also called DivIVA), Ftn2, or combinations thereof can disruptdivisome assembly, generally resulting in cell elongation.

By regulating cell size, the costs of cell mixing during culture and/orcell separation after culture can be reduced. For example, cell size canbe regulated in an inducible manner so that the costs of cell mixing canbe minimized during culture growth (e.g., by keeping cells small), andthe costs of harvesting can also be minimized by inducing cellelongation to facilitate cell separation and processing.

Cyanobacterial/Bacterial Cell Division

Cyanobacteria and bacteria have several genes that are involved in celldivision. Several of molecular players involved in cell division are asfollows.

-   -   FtsZ: This protein is a bacterial homolog of tubulin that is        needed for division of bacteria. FtsZ is able to polymerize into        filaments and laterally interact with other FtsZ filaments to        form an FtsZ-ring that constricts at the site of division. This        ring acts as the focal point for cell division by both providing        some constrictive force and by scaffolding other bacterial        division machinery.    -   MinC: This protein directly inhibits the self-assembly of FtsZ.        Therefore, FtsZ is most able to polymerize and form the        FtsZ-ring in areas of the cell where MinC is least active.    -   MinD: This protein binds to cell membranes and also recruits        MinC, thereby localizing MinC on the plasma membrane, near where        FtsZ polymers would form. Through recruiting MinC, it enhances        destabilization of FtsZ and also concentrates the MinC/MinD        destabilization at specific sites of action.    -   MinE: This protein stimulates the ATPase activity of MinD, which        causes MinD to dissociate from the membrane. The cooperative        action of many MinE proteins leads to the removal of MinD from        patches of the cell membrane. Collectively, MinE's interaction        with MinD leads to emergent behaviors that effectively “chase”        MinD from pole to pole, keeping the concentration of MinD (and        MinC) low in the center of the cell.    -   Cdv3: This protein has sequence homology to the bacterial        protein DivIVA and also shares some functional similarities. The        precise functions of Cdv3 were previously unclear. As        illustrated herein, if the levels of Cdv3 are too high (or too        low), cyanobacteria are unable to properly divide. Cdv3 is        recruited to the FtsZ-ring, and it can recruit a pool of MinC to        the FtsZ ring.

Cyanobacteria constitute a large phylum where Min dynamics that havepreviously not been studied in detail. Although, the cyanobacterial Mingenes share sequence homology with bacterial MinE and DivIVA (Cdv3)genes, cyanobacteria possess extensive, geometrically complex internalthylakoid membranes that could sequester MinCDE and/or complicateanalysis of the role of these genes in cell division. Hence, informationpreviously available for bacterial systems may not be applicable tocyanobacterial systems.

As described herein, the Min genes can modulate polymerization andlocalization of FtsZ, and the FtsZ protein is the protein that formscontractile Z rings that cause actual cell division. MinC can act as aninhibitor of Z-ring assembly. In wild type cells MinD recruits MinC ontoplasma membranes. MinE and Cdv3 (also called DivIVA) functionindependently in positioning MinCD, and hence Z rings, in rod-shapedcyanobacteria such as Synechococcus elongatus PCC 7942.

Methods are described herein to generate cyanobacterial populations thatcontain larger cells than wild type cyanobacterial populations of thesame species. Also described herein are cyanobacterial populations thatinclude a significant proportion of larger cells. Such larger cellpopulations can have expression cassettes or expression vectors withpromoters operably linked to nucleic acid segments encoding MinC, MinD,MinE, Cdv3 (DivIVA), and/or Ftn2 polypeptides.

Methods are also described herein to generate cyanobacterial populationsthat contain smaller cells than wild type cyanobacterial populations ofthe same species. Such methods can involve generating loss-of-functionmutations in MinC, MinD, MinE and/or Cdv3 (DivIVA) genes to generatecyanobacterial populations that contain smaller cells than wild typecyanobacterial populations of the same species. Moreover, overexpressionof FtsZ can reduce the mean cell size of cyanobacteria. Therefore, insome cases where smaller cell size is desirable, expression of FtsZ canbe induced. For example, cyanobacterial populations can containexpression cassettes or expression vectors with promoters operablylinked to nucleic acid segments encoding FtsZ, where the expression ofFtsZ can be regulated.

The wild type species described herein do not over-express MinC, MinD,MinE, Cdv3 (DivIVA), FtsZ and/or Ftn2 and do not have loss-of-functionmutations in MinC, MinD, MinE, Cdv3 (DivIVA), FtsZ and/or Ftn2 genes.

MinC

As indicated above, MinC proteins can stimulate depolymerization ofFtsZ. Therefore, FtsZ is most able to polymerize and form the FtsZ-ringin areas of the cell where MinC is least active. MinC proteinsparticipate in pole-to-pole oscillations that position the Z ring at thecell midzone.

As illustrated herein, in wild-type (WT) cells, cell sizes fell within anarrow range of about 1.7-4.5 μm (mean cell length 3.10±0.66 μm; FIG.2A-2B).

As also shown herein, cyanobacterial populations that overexpress MinCproteins have an increased mean cell size or length. To increasecyanobacterial or bacterial cell sizes a cell population of can bemodified to include an expression cassette or vector that encodes a MinCprotein. For example, the mean cell length of MinC overexpressingcyanobacterial cells is at least 150%, or at least 200%, or at least250%, or at least 300%, or at least 500%, or at least 750%, or at least1000%, or at least 5000%, or at least 10000%, or at least 15000%, or atleast 20000% greater than a wild type population of cyanobacteria of thesame species.

However, as demonstrated herein, cyanobacterial populations with loss offunction MinC mutations include cyanobacterial cells that aresignificantly smaller than are observed in wild type cyanobacterialpopulations of the same species. For example, the mean cell length ofMinC mutant cyanobacterial cells is at least 15%, or at least 20%, or atleast 25%, or at least 30%, or at least 35%, or at least 40%, or atleast 45%, or at least 50% less than the mean cell length of a wild typepopulation of cyanobacteria of the same species.

Examples of MinC sequences are provided herein to facilitate generationof cyanobacterial populations containing significant numbers of smallcells. One sequence for a Synechococcus elongatus MinC polypeptide hasthe following sequence (SEQ ID NO:4).

1 MSDVDASTPS AEEAIAPDID SDSDAAVETP AAEPAIAPPI 41QLEAEGDRWW LRLPSAPPVG QEANADGLTW LDLQQSLQQL 81LQGQENFWDA GAELHLFADS WLLDGRQLEW LSQQLARVDL 121KLTRITTQRR QTAVAAVSLG LSIEQPITQA DPWQRKTSTS 161PIAAPLYLKR TLRSGAEVRH NGSVIVVGDV NPGSSIVASG 201DILVWGNLRG IAHAGAAGNS DATIFALSLA ATQLRIGDRL 241ARLPSSQAAG YPETAQVIDG QIQIRRADPG GKA nucleic acid that encodes the polypeptide with SEQ ID NO:4 is shownbelow as SEQ ID NO:5.

1 ATGAGTGACG TAGACGCTTC TACCCCCTCG GCAGAGGAGG 41CGATCGCACC TGACATCGAC AGTGACAGCG ATGCGGCAGT 81TGAGACACCT GCTGCTGAAC CCGCGATCGC ACCGCCAATC 121CAGCTCGAAG CGGAGGGCGA TCGCTGGTGG TTGAGGCTGC 161CAAGTGCACC CCCGGTTGGT CAAGAAGCCA ATGCGGACGG 201CTTGACTTGG CTAGATTTGC AACAGTCGCT CCAACAATTG 241CTGCAAGGTC AGGAAAACTT CTGGGATGCG GGAGCTGAGC 281TCCACCTCTT TGCCGATAGT TGGCTACTGG ATGGGCGTCA 321GTTGGAATGG CTAAGCCAGC AGCTAGCGCG GGTTGACCTG 361AAATTGACAC GGATCACAAC CCAGCGCCGG CAGACGGCAG 401TGGCAGCCGT GAGCCTTGGG CTCTCGATTG AACAGCCAAT 441CACCCAGGCC GATCCTTGGC AGCGCAAGAC CTCGACCAGC 481CCCATTGCCG CGCCGCTCTA CCTCAAACGC ACCCTGCGAT 521CGGGAGCTGA GGTACGCCAT AACGGCTCAG TGATTGTGGT 561GGGAGATGTC AACCCCGGCA GCAGCATTGT GGCCAGTGGC 601GACATTCTTG TTTGGGGTAA CCTGCGGGGC ATTGCCCATG 641CGGGGGCTGC CGGTAATTCA GACGCGACAA TTTTTGCCCT 681GTCGCTGGCG GCCACCCAAC TGCGGATTGG CGATCGTCTA 721GCCAGACTGC CCAGTAGCCA AGCAGCCGGC TATCCCGAAA 761CGGCCCAAGT GATTGATGGT CAAATTCAGA TTCGCCGCGC 801 CGATCCTGGC GGGAAGTAG

Other cyanobacterial polypeptides and nucleic acids are available withsignificant sequence homology to the SEQ ID NO:4 MinC protein. SuchMinC-related sequences can be modified to include loss-of-functionmutations.

For example, a related Synechococcus elongatus MinC sequence withaccession number WP_050738292.1 (GI:914820796) is available from theNational Center for Biotechnology Information database (see website atncbi.nlm.nih.gov). The sequence for this MinC polypeptide shares 99% ormore sequence identity with SEQ ID NO:4 and is shown below as SEQ IDNO:6.

1 MSDVDASTPS AEEAIAPDID SDSDAAVEPP AAEPAIAPPI 41QLEAEGDRWW LRLPSAPPVG QEANADGLTW LDLQQSLQQL 81LQGQENFWDA GAELHLFADS WLLDGRQLEW LSQQLARADL 121KLTRITTQRR QTAVAAVSLG LSIEQPITQA DPWQRKTSTS 161PIAAPLYLKR TLRSGAEVRH NGSVIVVGDV NPGSSIVASG 201DILVWGNLRG IAHAGAAGNS DATIFALSLA ATQLRIGDRL 241ARLPSSQAAG YPETAQVIDG QIQIRRADPG GKA comparison between SEQ ID NO:4 and SEQ ID NO:6 MinC sequences is shownbelow. The asterisks below the comparison show which amino acids areidentical.99.3% identity in 272 residues overlap; Score: 1373.0; Gap frequency:0.0%

Seq4 1 MSDVDASTPSAEEAIAPDIDSDSDAAVETPAAEPAIAPPIQLEAEGDRWWLRLPSAPPVG Seq61 MSDVDASTPSAEEAIAPDIDSDSDAAVEPPAAEPAIAPPIQLEAEGDRWWLRLPSAPPVG**************************** ******************************* Seq4 61QEANADGLTWLDLQQSLQQLLQGQENFWDAGAELHLFADSWLLDGRQLEWLSQQLARVDL Seq6 61QEANADGLTWLDLQQSLQQLLQGQENFWDAGAELHLFADSWLLDGRQLEWLSQQLARADL********************************************************* ** Seq4 121KLTRITTQRRQTAVAAVSLGLSIEQPITQADPWQRKTSTSPIAAPLYLKRTLRSGAEVRH Seq6 121KLTRITTQRRQTAVAAVSLGLSIEQPITQADPWQRKTSTSPIAAPLYLKRTLRSGAEVRH************************************************************ Seq4 181NGSVIVVGDVNPGSSIVASGDILVWGNLRGIAHAGAAGNSDATIFALSLAATQLRIGDRL Seq6 181NGSVIVVGDVNPGSSIVASGDILVWGNLRGIAHAGAAGNSDATIFALSLAATQLRIGDRL************************************************************ Seq4 241ARLPSSQAAGYPETAQVIDGQIQIRRADPGGK Seq6 241ARLPSSQAAGYPETAQVIDGQIQIRRADPGGK ********************************

Another MinC sequence from Leptolyngbya sp. NIES-3755 is available fromthe NCBI database as accession number BAU11733.1 (GI:965632161), whichhas 46% sequence identity to SEQ ID NO:4, and is shown below as SEQ IDNO:7.

1 MTSDTSLSPL SNDPTPISPE AVSSPDVDAD LLDLPPLETP 41EVPKIAIEDL QVRLKAKDGV LSLILPPESE AASKVALAWG 61ELWQQLKQLL MGRERQWQPN TIVHLIADDR LLDTRQLSAI 121AEALTDVQLQ LKSVHTRRRQ TAVVAATAGY SVEQITAVDP 161LAAKQETAVA MEEPLYIQMT LRSGTEIRHN GTVVVMGDLN 201PGSTIIAEGD ILVWGRLRGV AHAGCKGNVK SLIMALQLEP 241TQIRIADYVA RAPETPPAQY FPEVAYVSPQ GSIRIARATD 281 FSMRKDDA comparison between SEQ ID NO:4 and SEQ ID NO:7 MinC sequences is shownbelow, with highly conserved amino acids identified. The asterisks belowthe comparison show which amino acids are identical.45.1% identity in 268 residues overlap; Score: 489.0; Gap frequency:2.6%

Seq4 5 DASTPSAEEAIAPDIDSD--SDAAVETPAAEPAIAPPIQLEAEGDRWWLRLPSAPPVGQE Seq713 DPTPISPEAVSSPDVDADLLDLPPLETPEVPKIAIEDLQVRLKAKDGVLSL-ILPPESEA*    * *    ** * *       ***          *         * *   ** Seq4 63ANADGLTWLDLQQSLQQLLQGQENFWDAGAELHLFADSWLLDGRQLEWLSQQLARVDLKL Seq7 72ASKVALAWGELWQQLKQLLMGRERQWQPNTIVHLIADDRLLDTRQLSAIAEALTDVQLQL*    * *  * * * *** * *  *      ** **  *** ***      *  * * * Seq4 123TRITTQRRQTAVAAVSLGLSIEQPITQADPWQRKTSTS-PIAAPLYLKRTLRSGAEVRHN Seq7 132KSVHTRRRQTAVVAATAGYSVEQ-ITAVDPLAAKQETAVAMEEPLYIQMTLRSGTEIRHN* ****** *   * * ** **  **   *  *      ***   ***** * *** Seq4 182GSVIVVGDVNPGSSIVASGDILVWGNLRGIAHAGAAGNSDATIFALSLAATQLRIGDRLA Seq7 191GTVVVMGDLNPGSTIIAEGDILVWGRLRGVAHAGCKGNVKSLIMALQLEPTQIRIADYVA* * * ** **** * * ******* *** ****  **    * ** *  ** ** *  * Seq4 242RLPSSQAAGY-PETAQVI-DGQIQIRRA Seq7 251 RAPETPPAQYFPEVAYVSPQGSIRIARA* *    * * ** * *   * * * **

Another MinC sequence from Gloeocapsa sp. PCC 7428 is available from theNCBI database as accession number WP_015191142.1 (GI:505004040), whichhas 46% sequence identity to SEQ ID NO:4, and is shown below as SEQ IDNO:8.

1 MTDSAPPEIE TTLTPPTNIA NSNLQVRLKG EGEHLLLILP 41TEVESSATAT TWSDLWQQLK QRLNGGDRFW QPNTIVHLMA 61TDRLLDTRQL QAIADALSEA QLQLTHVFTS RRQTAVAAAT 121AGYSVEQQAP ITGLNQTVNA APTPLAEPLY LQMTVRSGIE 161IRHAGSVIVL GDLNPGGTVV ANGDILVWGR LRGVAHAGAA 201GNSKCLIMAL QMEPTQLRIA EFVARAPTNI PSQFYPEVAY 241VTPEGIRIAK AADFSKSQFS LPSA comparison between SEQ ID NO:4 and SEQ ID NO:8 MinC sequences is shownbelow, with highly conserved amino acids identified. The asterisks belowthe comparison show which amino acids are identical.50.2% identity in 213 residues overlap; Score: 479.0; Gap frequency:1.9%

Seq4 58 PVGQEANADGLTWLDLQQSLQQLLQGQENFWDAGAELHLFADSWLLDGRQLEWLSQQLARSeq8 40 PTEVESSATATTWSDLWQQLKQRLNGGDRFWQPNTIVHLMATDRLLDTRQLQATADALSE*   *  *   ** ** * * * * *   **      ** *   *** ***      * Seq4 118VDLKLTRITTQRRQTAVAAVSLGLSIEQ--PITQADPWQRKTSTSPIAAPLYLKRTLRSG Seq8 100AQLQLTHVFTSRRQTAVAAATAGYSVEQQAPITGLNQTVNAAPT-PLAEPLYLQMTVRSG  * **   * ********   * * **  ***          * * * ****  * *** Seq4 176AEVRHNGSVIVVGDVNPGSSIVASGDILVWGNLRGIAHAGAAGNSDATIFALSLAATQLR Seq8 159IEIRHAGSVIVLGDLNPGGTVVANGDILVWGRLRGVAHAGAAGNSKCLIMALQMEPTQLR * ** ***** ** ***   ** ******* *** *********   * **    **** Seq4 236IGDRLARLPSS-QAAGYPETAQVIDGQIQIRRA Seq8 219IAEFVARAPTNIPSQFYPEVAYVTPEGIRIAKA *    ** *       *** * *    * *  *

Another MinC sequence from Leptolyngbya boryana IAM M-101 is availablefrom the NCBI database as accession number BAS56644.1 (GI:932876592),which has 50% sequence identity to SEQ ID NO:4, and is shown below asSEQ ID NO:9.

1 MTPDTSVSPT PIDPLSVTSD STLEKPLEAP TPSSDTPTAE 41NPKTDVTASS DAHASSEITD SSLSTSSELS PQTVAIADLQ 81VRLKTKEGEL HLILPPESEN SKIALAWVEL WQQFKQLLMG 121QERFWQPNTP VHLVSDDRLL DTRQISAIAE ALAEVQLQLK 161WVHTRRRQTA VVAATAGYSV EQITAASPLL PNSEPATAME 201DPLYIQMTLR SGAEIRHNGT VVVVGDLNPG SSIIAEGDIL 241VWGRLRGVAH AGCKGNAKCL IMALQMEPTQ IRIADYVARA 281PETPLAQYFP EVAYVSPQGS IRIARAADFA ARKEEPNFSA comparison between SEQ ID NO:4 and SEQ ID NO:9 MinC sequences is shownbelow, with highly conserved amino acids identified. The asterisks belowthe comparison show which amino acids are identical.48.6% identity in 212 residues overlap; Score: 485.0; Gap frequency:0.9%

Seq4 58 PVGQEANADGLTWLDLQQSLQQLLQGQENFWDAGAELHLFADSWLLDGRQLEWLSQQLARSeq9 95 PPESENSKIALAWVELWQQFKQLLMGQERFWQPNTPVHLVSDDRLLDTRQISAIAEALAE*   *     * *  * *   *** *** **      **  *  *** **       ** Seq4 118VDLKLTRITTQRRQTAVAAVSLGLSIEQPITQADPWQRKTSTSPIAAPLYLKRTLRSGAE Seq9 155VQLQLKWVHTRRRQTAVVAATAGYSVEQITAASPLLPNSEPATAMEDPLYIQMTLRSGAE* * *    * ****** *   * * **                   ***   ******* Seq4 178VRHNGSVIVVGDVNPGSSIVASGDILVWGNLRGIAHAGAAGNSDATIFALSLAATQLRIG Seq9 215IRHNGTVVVVGDLNPGSSIIAEGDILVWGRLRGVAHAGCKGNAKCLIMALQMEPTQIRIA **** * **** ****** * ******* *** ****  **    * **    ** ** Seq4 238DRLARLPSSQAAGY-PETAQVI-DGQIQIRRA Seq9 275DYVARAPETPLAQYFPEVAYVSPQGSIRIARA *  ** *    * * ** * *   * * * **

Another MinC sequence from Leptolyngbya boryana is available from theNCBI database as accession number WP_026148713.1 (GI:648456962), whichalso has 50% sequence identity to SEQ ID NO:4, and is shown below as SEQID NO:10.

1 MTDSSLSTSS ELSPQTVAIA DLQVRLKTKE GELHLILPPE 41 SENSKIALAW VELWQQFKQLLMGQERFWQP NTPVHLVSDD 81 RLLDTRQISA IAEALAEVQL QLKWVHTRRR QTAVVAATAG 121YSVEQITAAS PLLPNSEPAT AMEDPLYIQM TLRSGAEIRH 161 NGTVVVVGDL NPGSSIIAEGDILVWGRLRG VAHAGCKGNA 201 KCLIMALQME PTQIRIADYV ARAPETPLAQ YFPEVAYVSP241 QGSIRIARAA DFAARKEEPN FSA comparison between SEQ ID NO:4 and SEQ ID NO:10 MinC sequences isshown below, with highly conserved amino acids identified. The asterisksbelow the comparison show which amino acids are identical.48.6% identity in 212 residues overlap; Score: 485.0; Gap frequency:0.9%

Seq4 58 PVGQEANADGLTWLDLQQSLQQLLQGQENFWDAGAELHLFADSWLLDGRQLEWLSQQLARSeq10 38 PPESENSKIALAWVELWQQFKQLLMGQERFWQPNTPVHLVSDDRLLDTRQISAIAEALAE*   *     * *  * *   *** *** **      **  *  *** **       ** Seq4 118VDLKLTRITTQRRQTAVAAVSLGLSIEQPITQADPWQRKTSTSPIAAPLYLKRTLRSGAE Seq10 98VQLQLKWVHTRRRQTAVVAATAGYSVEQITAASPLLPNSEPATAMEDPLYIQMTLRSGAE * * *    ******* *   * * **                   ***   ******* Seq4 178VRHNGSVIVVGDVNPGSSIVASGDILVWGNLRGIAHAGAAGNSDATIFALSLAATQLRIG Seq10 158IRHNGTVVVVGDLNPGSSIIAEGDILVWGRLRGVAHAGCKGNAKCLIMALQMEPTQIRIA  **** ***** ****** * ******* *** ****  **    * **    ** ** Seq4 238DRLARLPSSQAAGY-PETAQVI-DGQIQIRRA Seq10 218DYVARAPETPLAQYFPEVAYVSPQGSIRIARA *  ** *    * * ** * *   * * * **

Any of the conserved amino acids and conserved domains illustrated bythe sequence comparisons shown above can be expressed in cells (e.g.,via a transgene or expression cassette introduced into a host cell) toincrease the activity of the MinC proteins described herein.

Any of the conserved amino acids and conserved domains illustrated bythe sequence comparisons shown above can also be deleted or mutated toreduce the activity of the (endogenous) MinC proteins described herein.

When reducing MinC expression, a wild type cyanobacterial population canhave a MinC polypeptide with at least 70%, or at least 75%, or at least80%, or at least 85%, or at least 90%, or at least 95%, or at least 97%,or at least 98%, or at least 99% sequence identity to any of SEQ IDNOs:4, 6-9, or 10.

Similarly, a cyanobacterial population can overexpress a MinCpolypeptide with at least 70%, or at least 75%, or at least 80%, or atleast 85%, or at least 90%, or at least 95%, or at least 97%, or atleast 98%, or at least 99% sequence identity to any of SEQ ID NOs:4,6-9, or 10. As illustrated herein, such overexpression can increase themean cell size or length of a cyanobacterial population.

However, cyanobacterial strains with reduced cell length can expressmutant MinC polypeptides that have reduced MinC activity. Such reducedactivity MinC polypeptides can have less than 99%, or less than 98%, orless than 95%, or less than 90%, or less than 85%, or less than 75%, orless than 60%, or less than 50%, or less than 40%, or less than 30%, orless than 20% sequence identity to any of SEQ ID NOs:4, 6-9, or 10. Themutations in mutant MinC polypeptides can, for example, have mutationsin at least one conserved amino acid position, or at least two conservedamino acid positions, or at least three conserved amino acid positions,or at least five conserved amino acid positions, or at least sevenconserved amino acid positions, or at least eight conserved amino acidpositions, or at least ten conserved amino acid positions, or at leastfifteen amino acid positions, or at least twenty conserved amino acidpositions, or at least twenty-five amino acid positions. In some cases,an entire conserved MinC domain or the entire endogenous MinC gene isdeleted or mutated (e.g., replaced with non-conserved sequences).

The conserved amino acids are in many cases mutated by deletion orreplacement with amino acids that have dissimilar physical and/orchemical properties (see, e.g., Table 1).

Such mutations can reduce MinC expression or function and providecyanobacterial populations with a mean cell length that is at least 10%smaller than the mean cell length of a wild type cyanobacterialpopulation of the same species.

In addition to mutations in the coding region of the MinC gene, theendogenous promoter that drives expression of MinC proteins can bemutated to reduce or eliminate MinC protein expression. One example of aSynechococcus elongatus minCD promoter sequence is shown below (SEQ IDNO:11).

1 AAATATTCTG AAATGAGCTG TTGACAATTA ATCATCCGGC 41 TCGTATAATG TGTGGA

To reduce expression of MinC protein, a promoter region with at least atleast 70%, or at least 75%, or at least 80%, or at least 85%, or atleast 90%, or at least 95%, or at least 97%, or at least 98%, or atleast 99% sequence identity to SEQ ID NO:11 can be mutated to reduce oreliminate transcription of MinC RNA. For example, a cyanobacterialpromoter with at least 75%, or at least 80%, or at least 85%, or atleast 90%, or at least 95%, or at least 97%, or at least 98%, or atleast 99% sequence identity to SEQ ID NO:11 can be mutated so that thepromoter sequence has less than 99%, or less than 98%, or less than 95%,or less than 90%, or less than 85%, or less than 75%, or less than 60%,or less than 50%, or less than 40%, or less than 30%, or less than 20%sequence identity to SEQ ID NO:11. In some cases such a cyanobacterialpromoter can have a deletion of at least one nucleotide, or at least twonucleotides, or at least three nucleotides, or at least fivenucleotides, or at least ten nucleotides, or at least twentynucleotides, or at least twenty five nucleotides, or at least thirtynucleotides. Such deletions can reduce MinC expression and providecyanobacterial populations with a mean cell length that is at least 10%smaller than the mean cell length of a wild type cyanobacterialpopulation of the same species.

In some cases, MinC mutations are introduced by insertion of foreign DNAinto the gene of interest such as transposable elements or T-DNA. Theforeign DNA not only disrupts the expression of the gene into which itis inserted but also acts as a marker for subsequent identification ofthe mutation. For example, the insertion of a transposon or T-DNA on theorder of 5 to 25 kb in length generally produces a dramatic disruptionof gene function. If a large enough population of transposon-transformedor T-DNA-transformed lines is available, one has a very good chance offinding a cyanobacteria carrying an insertion within any gene ofinterest.

Insertion, modification, or deletion of MinC mutations can involve useof a targeting vector that contains MinC homologous flanking sequences.For example, the following two flanking regions of the Synechococcuselongatus MinC gene can be employed to generate insertion, modification,or deletion MinC mutations. The first MinC flanking region is referredto as ΔminC Region 1 and is assigned SEQ ID NO:12.

1 AGTCTAGGGA TCAGCATTGG GAAAAAACCT GAATGGATAG 41 GGCTCGTGGG GTTGAGTGCTCTAAGCAGAC TCATAGGGGG 81 TACGAACCCA ATTCGGTTTT GGATGCATCG ATCGCTGGCA 121ATTAATCCGA ACGAGTTGCG GTGACAGGGG GTTGCGATCG 161 CCGACGAGGC TTGGGCCGAAAGGGGACCAG CAGTTCTGCC 201 TCAACAATCC GCAACTGACC GTACCGAGTC ACCTCGCAGT241 CAAACTGCCA CCACCCTGGA CGCAGTTGCT CAGGTGCCCC 281 GCGCAATTGCAGTCGTTTGA TTTTCCAGGC TGGCTTGTCG 321 ATCTGTCCGG GTGGCGCGGC CTCATTGCGACCAATCCAGA 361 CCTGCACGGC CCCGTTTTGA TCCTTCCAGC TTTTGACAAA 401ACCGCAGATC CGTACCCGAC CAGCTTGTAG ATCTGCGGGA 441 GCCTGATTTT GCCAGCCCCGCAACCAAAAT TGCAGATGCT 481 TGTGGCGTTG CAGCGGCCAG CTGACCCAGT AGTGAGGGGT521 TTGCATGAGC TGCTGCAGCT GCTGGGGATG GCGTTGTAGG 561 GTCGCTTGCACCAATCCACT CAGCGCTACA TTCAGGCTGT 601 GATTGTCCGT AATCTGCAGA GTGGCTGTTTCTCCCTGTTG 641 GTCCCAAGCC AAGCTGCCTT GGAAACAAGC AACCGCCCGA 681TAGGTGACGC TGTCGGGCTT CGGGGGCAGT TCCGTGCGGC 721 GGGGTGGCTT GCGGCTGGGACGCGATCGCG ACGCAGCAGG 761 GCTAGAACGG GTGATCGGTC GCGCAGGGCG TGGACGACCA801 CTCGGCAAAG GGGATGGGGG AGGCGTAGCC ATGGATGGCA 841 CTGGGCAAGGGCGATCACTG TTATTCTGGC GGCTCCCGCT 881 CGACTTGCCC GTACTCTTTA ATTTGTTTTGGGCTAAATAT 921 CGGGCCAAGT CTGCTTGGGC AGCGGATCTC TGGATCCATC 961CCAGCCCAAT TGCTAACCTG CTCTCTACCC CGTGGTTCCGThe second MinC flanking region is referred to as ΔminC Region 2 and isassigned SEQ ID NO:13.

1 GGGCACATCT TGAGACGATC GCCCGATGCG ACCGCTTCGC 41 GGAGTGAACC TTCGACTGAACCTTAGCGCC CGCCAAAATG 81 CAAAACTGAC AGAGAGCCTG TCCTGCTCTG TCCTACTTCC 121GTTTCAATAC TGTTTCACCT GCAAAGGTGC TTTTCCTAGG 161 TTGGCAGATG AGCGATCGCCCGCAGCCGGC ACCCACCGTC 201 CTGAAACGCC TGACCCAATT GGCAACGCAG GTTCAGCGAC241 GGGCCAAGTT TGATAATCTC AACCTGCGTG ACTCTGACTC 281 AGTTCCCCAATTGACGGTCT GTCAGGGAGA CCGCCGGCAG 321 TCTTATCCGC TGCTTGGGGA CTATTACCGCCTGGGCCGAG 361 GCCGTGACTG TGACATCCCG ATTGATAGCC CGATCGTCAG 401CAAGCTTCAC CTCAGCCTCG GTCGCTCGGG CAAAGAGCGC 441 GGTGACTTTG TCCTGCAAGACGAAAACTCG ACCAACGGCG 481 TCTTTTGGCG GGGCCGCCGT GTCGATCGCT TGGAATTACA521 GCATGGCGAT CGCATCTACC TGGGGCCACC AGAGCTGACC 561 GATCGCGTTGAGCTGCTCTA TGAAAACGCT CCTCCTCTCT 601 GGCAGGACTG GCTGAAACGA GGGGTGACTATCACTACAGC 641 TGTGGTCGGA GCGATCGCGA TCGGCATTAC CCTCGAGGCC 681AGCCGAGTCT CCGTGCGATC GCTGGGGACG GTGCAAGGAC 721 CGATCGCTGC CTATGCCGCTGATGGCGAGC CCCTACAAAC 761 TCTGCGCAGT AGTAGCCACG TCGAATTACC GGCCCTCTCA801 GATTTTTCGC CCGTTCTCCC CAAAGCCCTG CTTGCCTCCG 841 AAGACAGTCGCTTCTACTGG CATCTGGGTA TCGATCCCTA 881 CGGCACGGCG CGTGCGATTC TGACTAACTTCCGCAGTGGC 921 GAAGTTCGCG AAGGCGCCAG CACCCTCACC CAGCAGATTG 941CTCGCAGCCT ATTTAGCGAC TACGTCGGGC GTGAGGACTCMutations can be generated in MinC sequences from a variety ofcyanobacterial species, for example, by transforming cells from theselected cyanobacterial species with a targeting vector that includestwo flanking segments, for example, SEQ ID NO:12 and 13 in Synechococcuselongatus and related cyanobacterial species. Such targeting vectors canbe used for cyanobacterial species other than Synechococcus elongatus,for example, by using targeting vectors that have flanking segmentsequences that have less than 100%, or less than 99%, or less than 98%,or less than 95%, or less than 90%, or less than 85%, or less than 75%sequence identity to SEQ ID NO:12 and/or 13, but still retain somesequence identity to SEQ ID NO:12 and/or 13. In some cases the targetingvectors that have flanking segment sequences that have at least 70%, orat least 75%, or at least 80%, or at least 85%, or at least 90%, or atleast 95%, or at least 97%, or at least 98%, or at least 99% sequenceidentity to SEQ ID NOs:12 and 13.

Such mutations can reduce MinC expression or function and providecyanobacterial populations with a mean cell length that is at least 10%smaller than the mean cell length of a wild type cyanobacterialpopulation of the same species.

In some cases, to induce expression of MinC protein, a promoter regioncan be used in an expression cassette or vector where the promoter hasat least at least 70%, or at least 75%, or at least 80%, or at least85%, or at least 90%, or at least 95%, or at least 97%, or at least 98%,or at least 99% sequence identity to SEQ ID NO:11.

MinD Sequences

MinD proteins bind to the cell membrane and interact with both MinC andMinE proteins, and promote the function of MinC. As illustrated herein,cyanobacterial populations that overexpress MinD proteins have anincreased mean cell size or length. For example, the mean cell length ofMinD overexpressing cyanobacterial cells is at least 150%, or at least200%, or at least 250%, or at least 300%, or at least 500%, or at least750%, or at least 1000%, or at least 5000%, or at least 10000%, or atleast 15000%, or at least 20000% greater than a wild type population ofcyanobacteria of the same species.

However, as also demonstrated herein, cyanobacterial populations withloss of function MinD mutations include cyanobacterial cells that aresignificantly smaller than are observed in wild type cyanobacterialpopulations of the same species. For example, the mean cell length ofMinD mutant cyanobacterial cells mean cell length is at least 15%, or atleast 20%, or at least 25%, or at least 30%, or at least 35%, or atleast 40%, or at least 45%, or at least 50% less than a wild typepopulation of cyanobacteria of the same species.

Examples of MinD sequences are provided herein to facilitate generationof cyanobacterial populations containing significant numbers of large orsmall cells. One sequence for a Synechococcus elongatus MinD polypeptidehas the following sequence (SEQ ID NO:14).

1 MSRVIVVTSG KGGVGKTTSS ANLGMALAQL GKRLVLIDAD 41 FGLRNLDLLL GLENRIVYTAQDVLAGNCRL EQALVKDKRQ 81 PNLCLLPAAN NRMKESVTPQ QMEQLVTLLD GQFDVILIDS 121PAGIEAGFQN AIAAAREAVI VTTPEIAAVR DADRVIGLLE 161 AHGITEIRLI LNRLRPAMVKANDMMSVEDV QEILAIPLVG 201 IIPDDEQVII STNRGEPLVL AEAPSLAAKA FINVARRLSG241 ESIDFLNLEE PQSGVLSKIR RILNKKILA nucleic acid that encodes the polypeptide with SEQ ID NO:14 has thesequence shown below as SEQ ID NO:15.

1 ATGAGTCGCG TTATTGTTGT CACCTCCGGT AAGGGAGGCG 41 TGGGCAAAAC CACCTCCAGCGCCAACTTGG GTATGGCCTT 81 AGCCCAGCTG GGTAAACGCC TCGTGCTCAT CGATGCGGAC 121TTTGGCTTGC GCAATCTCGA CCTGCTGCTG GGGCTGGAGA 161 ATCGGATTGT CTACACCGCTCAGGATGTTT TAGCGGGCAA 201 TTGCCGCCTC GAGCAAGCAT TGGTCAAAGA CAAGCGCCAA241 CCGAATCTCT GCCTGCTGCC TGCGGCCAAC AACCGCATGA 281 AGGAGTCGGTGACCCCCCAG CAGATGGAGC AGTTGGTGAC 321 GCTGCTCGAT GGTCAGTTCG ACGTGATCTTGATCGACTCA 361 CCCGCTGGAA TTGAAGCCGG ATTCCAGAAT GCGATCGCGG 401CCGCCCGCGA AGCCGTAATT GTTACGACGC CGGAGATTGC 441 GGCTGTCCGA GACGCCGATCGCGTTATTGG ATTGCTAGAA 481 GCCCATGGCA TCACAGAGAT TCGGCTGATT TTGAACCGGC521 TGCGGCCAGC GATGGTCAAG GCCAACGACA TGATGAGTGT 561 CGAAGATGTGCAGGAAATCC TCGCGATCCC TCTTGTCGGC 601 ATCATTCCCG ATGACGAGCA GGTGATTATTTCCACCAACC 641 GTGGCGAGCC GTTGGTCCTA GCCGAGGCAC CTTCCTTGGC 681GGCCAAGGCA TTCATCAATG TGGCGCGGCG CCTGAGTGGT 721 GAAAGCATCG ACTTCCTCAATCTTGAGGAA CCCCAGAGCG 761 GTGTGCTCAG TAAGATTCGC CGCATCCTCA ATAAAAAAAT801 TCTCTAG

Other cyanobacterial polypeptides and nucleic acids are available withsignificant sequence homology to the SEQ ID NO:14 MinD protein. Forexample, a related Oscillatoriales cyanobacterium JSC-12 MinD sequencewith accession number WP_009769434.1 (GI:497455236) is available fromthe National Center for Biotechnology Information database (see websiteat ncbi.nlm.nih.gov). The sequence for this MinD polypeptide shares 74%or more sequence identity with SEQ ID NO:14 and is shown below as SEQ IDNO:16.

1 MSRVIVVTSG KGGVGKTTTT ANLGMALAKR GRKVIVIDAD 41 FGLRNLDLLL GLENRVVYTAVDVLAGQCRL EQALVKDKRH 81 PNLMLLPAAQ NRTKDAVKPD QMKQLVNALA KAFNYVLVDC 121PAGIEMGFQN AIAAAKEALI VTTPEIAAVR DADRVVGLLE 161 ANNIKQIRLI VNRLRPAMVQANDMMTVEDV QEILAVPLIG 201 IVPDDERVIV STNKGEPLVL AETPSLAGTA FDNIARRLEG241 ESVEFLDFTA PNDGFFSRLR RVLTTPIGKK PSKA comparison between SEQ ID NO:14 and SEQ ID NO:16 MinD sequences isshown below, with highly conserved amino acids identified. The asterisksbelow the comparison show which amino acids are identical.73.8% identity in 267 residues overlap; Score: 1008.0; Gap frequency:0.0%

Seq14 1 MSRVIVVTSGKGGVGKTTSSANLGMALAQLGKRLVLIDADEGLRNLDLLLGLENRIVYTASeq16 1 MSRVIVVTSGKGGVGKTTTTANLGMALAKRGRKVIVIDADEGLRNLDLLLGLENRVVYTA******************  ********  *     ******************* **** Seq14 61QDVLAGNCRLEQALVKDKRQPNLCLLPAANNRMKESVTPQQMEQLVTLLDGQFDVILIDS Seq16 61VDVLAGQCRLEQALVKDKRHPNLMLLPAAQNRTKDAVKPDQMKQLVNALAKAFNYVLVDC  ***************** *** ***** ** *  * * ** ***  *   *   * * Seq14 121PAGIEAGFQNAIAAAREAVIVTTPEIAAVRDADRVIGLLEAHGITEIRLILNRLRPAMVK Seq16 121PAGIEMGFQNAIAAAKEALIVTTPEIAAVRDADRVVGLLEANNIKQIRLIVNRLRPAMVQ ************** ** **************** *****  *  **** ******** Seq14 181ANDMMSVEDVQEILAIPLVGIIPDDEQVIISTNRGEPLVLAEAPSLAAKAFINVARRLSG Seq16 181ANDMMTVEDVQEILAVPLIGIVPDDERVIVSTNKGEPLVLAETPSLAGTAFDNIARRLEG ************** ** ** **** ** *** ******** ****  ** * **** * Seq14 241ESIDFLNLEEPQSGVLSKIRRILNKKI Seq16 241 ESVEFLDFTAPNDGFFSRLRRVLTTPI**  **    *  *  *  ** *   *

Another MinD sequence from Kamptonema is available from the NCBIdatabase as accession number WP_007353741.1 (GI:494595482), which has atleast 72% sequence identity to SEQ ID NO:14, and is shown below as SEQID NO:17.

1 MARIIVVTSG KGGVGKTTST ANLGMALAKL GRSVAVVDAD 41 FGLRNLDLLL GLENRIVYTAVEVIAGECRL EQALVKDKRQ 81 PNLVLLPAAQ NRMKDAVSAE QMKQLVNVLA EKYDYILIDS 121PAGIEQGFQN AIAAAQEGVI VTTPEIAAVR DADRVVGLLE 161 AHNVKRIHLI VNRIRPLMVQANDMMSVQDV REILAIPLLG 201 VVPDDERVIV STNRGEPLVL SETPSLAGTA YENIARRLEG241 EKVEFLELNP PQDNFFTRLR RLLTAKIMA comparison between SEQ ID NO:14 and SEQ ID NO:17 MinD sequences isshown below, with highly conserved amino acids identified. The asterisksbelow the comparison show which amino acids are identical.72.4% identity in 268 residues overlap; Score: 1005.0; Gap frequency:0.0%

Seq14 1 MSRVIVVTSGKGGVGKTTSSANLGMALAQLGKRLVLIDADEGLRNLDLLLGLENRIVYTASeq17 1 MARIIVVTSGKGGVGKTTSTANLGMALAKLGRSVAVVDADFGLRNLDLLLGLENRIVYTA * **************** ******** **      *********************** Seq14 61QDVLAGNCRLEQALVKDKRQPNLCLLPAANNRMKESVTPQQMEQLVTLLDGQFDVILIDS Seq17 61VEVIAGECRLEQALVKDKRQPNLVLLPAAQNRMKDAVSAEQMKQLVNVLAEKYDYILIDS   * ****************** ***** ****  *   ** ***  *    * ***** Seq14 121PAGIEAGFQNAIAAAREAVIVTTPEIAAVRDADRVIGLLEAHGITEIRLILNRLRPAMVK Seq17 121PAGIEQGFQNAIAAAQEGVIVTTPEIAAVRDADRVVGLLEAHNVKRIHLIVNRIRPLMVQ ************** * ***************** ******    * ** ** ** ** Seq14 181ANDMMSVEDVQEILAIPLVGIIPDDEQVIISTNRGEPLVLAEAPSLAAKAFINVARRLSG Seq17 181ANDMMSVQDVREILAIPLLGVVPDDERVIVSTNRGEPLVLSETPSLAGTAYENIARRLEG ******* ********* *  **** ** ********** * ****  *  * **** * Seq14 241ESIDFLNLEEPQSGVLSKIRRILNKKIL Seq17 241 EKVEFLELNPPQDNFFTRLRRLLTAKIM*   ** *  **       ** *  **

Another MinD sequence from Geitlerinema sp. PCC 7407 is available fromthe NCBI database as accession number WP_015173510.1 (GI:504986408),which also has at least 72% sequence identity to SEQ ID NO:14, and isshown below as SEQ ID NO:18.

1 MSRVIVVTSG KGGVGKTTCT ANLGMALAQQ GRRVIVVDAD 41 FGLRNLDLLL GLENRIVYTALEVLAGECRL EQAIVKDKRQ 61 NRLALLPAAQ NRTKDAVRPE QMKQLIAALT GKYDYILVDC 121PAGIEMGFQN AIVAAREALV VTTPEISAVR DADRVVGLLE 161 AQGIKQMRLI INRIRPNMVQVNDMMSVEDV QEILAIPLIG 201 VIPDDERVIV STNRGEPLVL SETPSMAGTA FENVARRLEG241 QKVEFLDLNG PGDSFFSRIK RLLSTKILA comparison between SEQ ID NO:14 and SEQ ID NO:18 MinD sequences isshown below, with highly conserved amino acids identified. The asterisksbelow the comparison show which amino acids are identical.72.4% identity in 268 residues overlap; Score: 1000.0; Gap frequency:0.0%

Seq14 1 MSRVIVVTSGKGGVGKTTSSANLGMALAQLGKRLVLIDADEGLRNLDLLLGLENRIVYTASeq18 1 MSRVIVVTSGKGGVGKTTCTANLGMALAQQGRRVIVVDADEGLRNLDLLLGLENRIVYTA******************  ********* * *    *********************** Seq14 61QDVLAGNCRLEQALVKDKRQPNLCLLPAANNRMKESVTPQQMEQLVTLLDGQFDVILIDS Seq18 61LEVLAGECRLEQAIVKDKRQNRLALLPAAQNRTKDAVRPEQMKQLIAALTGKYDYILVDC   ********** ******  * ***** ** *  * * ** **   * *  * ** * Seq14 121PAGIEAGFQNAIAAAREAVIVTTPEIAAVRDADRVIGLLEAHGITEIRLILNRLRPAMVK Seq18 121PAGIEMGFQNAIVAAREALVVTTPEISAVRDADRVVGLLEAQGIKQMRLIINRIRPNMVQ *********** *****  ****** ******** ***** **   *** ** ** ** Seq14 181ANDMMSVEDVQEILAIPLVGIIPDDEQVIISTNRGEPLVLAEAPSLAAKAFINVARRLSG Seq18 181VNDMMSVEDVQEILAIPLIGVIPDDERVIVSTNRGEPLVLSETPSMAGTAFENVARRLEG ***************** * ***** ** ********** * ** *  ** ****** * Seq14 241ESIDFLNLEEPQSGVLSKIRRILNKKIL Seq18 241 QKVEFLDLNGPGDSFFSRIKRLLSTKIL    ** *  *     * * * *  ***

Another MinD sequence from Planktothricoides sp. SR001 is available fromthe NCBI database as accession number WP_054465548.1 (GI:935599625),which has 73% sequence identity to SEQ ID NO:14, and is shown below asSEQ ID NO:19.

1 MSRIIVITSG KGGVGKTTST ANLGMALAKR GRKVALIDAD 41 FGLRNLDLLL GLENRIVYTAVEVIAGQCRL EQALVKDKRQ 81 PGLALLPAAQ NRMKDAVTPD QMKQIVQQLL QKYHYVLIDS 121PAGIEQGFQN AIAAAREALI VTTPEIAAVR DADRVIGLLE 161 AHGVRQIHLI VNRLKPQMVEANDMMSVADV QEILAIPLIG 201 VIPDDERVIV STNRGEPLVL GEEQTLAGKA FDNIARRLEG241 EKVELLDLSL PSDNFFSRIR KLFFTKIMA comparison between SEQ ID NO:14 and SEQ ID NO:19 MinD sequences isshown below, with highly conserved amino acids identified. The asterisksbelow the comparison show which amino acids are identical.73.1% identity in 268 residues overlap; Score: 993.0; Gap frequency:0.0%

Seq14 1 MSRVIVVTSGKGGVGKTTSSANLGMALAQLGKRLVLIDADEGLRNLDLLLGLENRIVYTASeq19 1 MSRIIVITSGKGGVGKTTSTANLGMALAKRGRKVALIDADEGLRNLDLLLGLENRIVYTA ***** ************ ********  *    ************************* Seq14 61QDVLAGNCRLEQALVKDKRQPNLCLLPAANNRMKESVTPQQMEQLVTLLDGQFDVILIDS Seq19 61VEVIAGQCRLEQALVKDKRQPGLALLPAAQNRMKDAVTPDQMKQIVQQLLQKYHYVLIDS   * **************** * ***** ****  *** ** * *  *       **** Seq14 121PAGIEAGFQNAIAAAREAVIVTTPEIAAVRDADRVIGLLEAHGITEIRLILNRLRPAMVK Seq19 121PAGIEQGFQNAIAAAREALIVTTPEIAAVRDADRVIGLLEAHGVRQIHLIVNRLKPQMVE ***************** ************************   * ** *** * ** Seq14 181ANDMMSVEDVQEILAIPLVGIIPDDEQVIISTNRGEPLVLAEAPSLAAKAFINVARRLSG Seq19 181ANDMMSVADVQEILAIPLIGVIPDDERVIVSTNRGEPLVLGEEQTLAGKAFDNIARRLEG ***************** * ***** ** ********** *   ** *** * **** * Seq14 241ESIDFLNLEEPQSGVLSKIRRILNKKIL Seq19 241 EKVELLDLSLPSDNFFSRIRKLFFTKIM*    * *  *     * **     **

Any of the conserved amino acids and conserved domains illustrated bythe sequence comparisons shown above can be expressed in cells (e.g.,via a transgene or expression cassette introduced into a host cell) toincrease the activity of the MinD proteins described herein.

In addition, any of the conserved amino acids and conserved domainsillustrated by the sequence comparisons shown above can be deleted toreduce the expression and/or activity of the (e.g., endogenous) MinDproteins described herein.

To increase cyanobacterial or bacterial cell sizes a cell population ofcan be modified to include an expression cassette or vector that encodesa MinD polypeptide. For example, an expression cassette or vector thatencodes a MinD polypeptide can have at least 70%, or at least 75%, or atleast 80%, or at least 85%, or at least 90%, or at least 95%, or atleast 97%, or at least 98%, or at least 99% sequence identity to any ofSEQ ID NOs:14, 16, 17, 18, or 19.

In some cases, cyanobacterial cell population can be of reduced cellsizes. For example, MinD mutations can be introduced to reduce cell sizeby methods that can include deletion or insertion of foreign DNA intothe MinD locus. For example, this can involve the use of eithertransposable elements or T-DNA. The foreign DNA not only disrupts theexpression of the gene into which it is inserted but also acts as amarker for subsequent identification of the mutation. If a large enoughpopulation of transposon-transformed or T-DNA-transformed lines isavailable, one has a very good chance of finding a cyanobacteriacarrying an insertion within any gene of interest.

Any of the conserved amino acids and conserved domains illustrated bythe sequence comparisons shown above can be deleted or mutated to reducethe activity of the MinD proteins described herein.

For example, a wild type cyanobacterial population can have a MinDpolypeptide with at least 70%, or at least 75%, or at least 80%, or atleast 85%, or at least 90%, or at least 95%, or at least 97%, or atleast 98%, or at least 99% sequence identity to any of SEQ ID NOs:14,16, 17, 18, or 19.

However, the cyanobacterial strain with reduced cell length can expressmutant MinD polypeptides that have reduced MinD activity. Such MinDpolypeptides that have reduced MinD activity can have less than 99%, orless than 98%, or less than 95%, or less than 90%, or less than 85%, orless than 75%, or less than 60%, or less than 50%, or less than 40%, orless than 30%, or less than 20% sequence identity to any of SEQ IDNOs:14, 16, 17, 18, or 19. The mutations in mutant MinC polypeptidescan, for example, have mutations in at least one conserved amino acidposition, or at least two conserved amino acid positions, or at leastthree conserved amino acid positions, or at least five conserved aminoacid positions, or at least seven conserved amino acid positions, or atleast eight conserved amino acid positions, or at least ten conservedamino acid positions, or at least fifteen amino acid positions, or atleast twenty conserved amino acid positions, or at least twenty-fiveamino acid positions. In some cases, an entire conserved MinD domain orthe entire endogenous MinD gene is deleted or mutated.

The conserved amino acids are in many cases mutated by deletion orreplacement with amino acids that have dissimilar physical and/orchemical properties.

In addition to mutations in the coding region of the MinD gene, theendogenous promoter that drives expression of MinD proteins can bemutated to reduce or eliminate MinD protein expression. As describedabove, one example of a Synechococcus elongatus minCD promoter sequenceis shown below (SEQ ID NO:20).

1 AAATATTCTG AAATGAGCTG TTGACAATTA ATCATCCGGC 41 TCGTATAATG TGTGGA

To reduce expression of MinD protein, a promoter region with at least atleast 70%, or at least 75%, or at least 80%, or at least 85%, or atleast 90%, or at least 95%, or at least 97%, or at least 98%, or atleast 99% sequence identity to SEQ ID NO:20 can be mutated to reduce oreliminate transcription of MinD RNA. For example, a cyanobacterialpromoter with at least 75%, or at least 80%, or at least 85%, or atleast 90%, or at least 95%, or at least 97%, or at least 98%, or atleast 99% sequence identity to SEQ ID NO:20 can be mutated be mutated sothat the promoter sequence has less than 99%, or less than 98%, or lessthan 95%, or less than 90%, or less than 85%, or less than 75%, or lessthan 60%, or less than 50%, or less than 40%, or less than 30%, or lessthan 20% sequence identity to SEQ ID NO:20. In some cases such acyanobacterial promoter can have a deletion of at least one nucleotide,or at least two nucleotides, or at least three nucleotides, or at leastfive nucleotides, or at least ten nucleotides, or at least twentynucleotides, or at least twenty five nucleotides, or at least thirtynucleotides. Such deletions can reduce MinD expression and providecyanobacterial populations with a mean cell length that is at least 10%smaller than the mean cell length of a wild type cyanobacterialpopulation of the same species.

In some cases, MinD mutations are introduced by insertion of foreign DNAinto the gene of interest. For example, this can involve the use ofeither transposable elements or T-DNA. The foreign DNA not only disruptsthe expression of the gene into which it is inserted but also acts as amarker for subsequent identification of the mutation. The insertion of atransposon or T-DNA on the order of 5 to 25 kb in length generallyproduces a dramatic disruption of gene function. If a large enoughpopulation of transposon-transformed or T-DNA-transformed lines isavailable, one has a very good chance of finding a cyanobacteriacarrying an insertion within any gene of interest.

Insertion, modification, or deletion of MinD mutations can involve useof a targeting vector that contains MinD homologous flanking sequences.For example, the following two flanking regions of the Synechococcuselongatus MinD gene can be employed to generate insertion, modification,or deletion MinD mutations. The first MinD flanking region is referredto as ΔminD Region 1 and assigned SEQ ID NO:21.

1 GGCGGGCTTG GGCTTCTGTC AGTCCTACCT GAGCTGCCGC 41CGGATCCATC TCTAAAACTT GCTGCGGGGC TAGAGCTGAT 81TGCTGACGCG GCCAACCGAA CAGACCGTGT TGCGCGATCG 121CACGGACTTC TGCCGGACTG AGATTGGCTG CGATCGCCCG 161ACTCCCCGGC AGCAGCGGCA GCGGATCAGG TTGGAAATAA 201TTGAGACTCA GCTCGCAGGA ATCCGTCTGA CGAGTTGACT 241GCTCCAGCAG ATGGATGCCC TCAGCCTGAC ATTGAGCTTG 281CAGCCGTTGA ACAATCGTAG GCTCCCAACT CGACCAGATT 321GCAGGCGTTG CCAAGCCGAC ATCCCAACCA TGACGGGTCA 441GGGCTTGGGC AACTCCAATC GCGATTGTGC GATCGCCAGT 481AACCGTCACA GATTGCGGTT GTGGATCGGC GGTCAGTAAG 521TCCCAGAGCG GCGTTGCTTC TGCCCCTGTC GGTTGAGCCT 561GCCAGATCTG CCGCGCCTCC AGTCGGCGAT CGCTACAGTC 601CACCACCCGA CGCGATCGTG TCGCTTTCCA GTGACTGGCA 641ACAATATCAA TTCCCTGTTG CTGCAGAGCG ATCGGGCCTT 681GCAGTAGCTC AAGGCGTTCG TAGAGAGCCT GCCCTGAGGC 721CAGTGCTTCT GGGACAGAAG TGGACTTCAA CAAGCAACGC 801ATCAACAGGC GATCGCGATC GATCGCGCCC CAACTCTCTG 841GCAGATAGAT CAAGGCCACA CGAGCCTGCC AGCGCCGTGC 881CTGTTGTGCC AGCGCGATCG CTGCCGGTGT CGCCCCCAGA 921ATCAGTAAGT TATAGTCCGC TGTCATTCAA GTTGGGAGTG 961AAAGCCCCGC TGCATTGTCT TTCCATCGTC AGGCAGAACA 1001GCCCTGTCAT GAAGGGTGAA TATAGAAAGC CTTTGGCAGT 1041CTAGGGGGAT TTGACGACAC GGTTTAAGAT GAGTCAGCGA 1081TTGCCGGCTG AGCGATCGCC GCTCCTGCTC TTCGGACCCTThe second MinD flanking region is referred to as ΔMinD Region 2 and isassigned SEQ ID NO:22.

1 TAATTACTGC CTTGCCGGTG TAGCTCAGGG GTAGAGCAGC 41TGTTTTGTAA ACAGCCGGTC GCAGGTTCGA ATCCGGTCAC 81CGGCTCTGAG CTCAAACCCA GTCTTCTTGT TGGAGGCTGG 121GTTTTTGTTT GTCGTAGCTG ACTAGACGTT CCCTGCCGTA 161ACCACGGATT GCTGACTGAA TCAAGCCGCT TCAGAGATGT 201CATCCGTGCG AGTCAGTGTC AGGGCGTAAC GGTAGAGCGC 241GATCGGACGA TCGCCAACTT GAAAGTAGCT GGGGTCCTGC 281GGCGTCAGAT AGATGGCGGT AATTTGATCC GCCGTAATCA 321AATTGGGCGA TCGCAGCTGG TAGCGAGCTG TGGTTTCTAC 361GCTGTTGAAC TGAGGGCGAC CCTGACCCCG AAAAATCTGG 401CGGCTCAGTT CGCTAGCAAT GAAAACGAAG TCGGTGGGCT 441GTTCCCAGGC TCGGCCTGTC ATCCGCATTA GCAGACTATC 481GCCATTCACC AACTGGACGA GTTGTTGATT GGGATCAGGA 521GCTTTGACGG TGGCAACAGC CTCCCCAAGA TAGGCGCGGG 561CGATCGCAAG GCCATTAAAA GCGCGATCGG CGACGACGGG 601GGCTGCTTGA GGCCGTAAAT CTGGTAGCGG TTTTGCAGCG 641GCAGCGTAGG TCGGGGTGCC AAAGCGCACA GGAAACTCCA 681GCGGTTGATC CAGCCAGCGG CGATTGCTGT CAAAGCCTGG 721TGTGATGATT TCCGGCGCGA GGGGTGCTTG TAAATCCACC 761AAGGTGCTGG TGACTTGCCA CGTTCCTGCC ATCCAATCGG 801GGTAGGGCAG ATCCGGTGCA TTGGTTTTTA GGGATGGTGA 841GCTTGACCAA GCCGGATACG ACGCAACGCG ATCGCTCAAG 881GTTGCCGCCT GTGCTGGTGT GATCACAGTC AGCCAACAGC 921CGAGGGCAAT CGCTCCGATT AACAGCGATC GCAGTAACCC 961AACAGGAACA ACACGCACGA CAAATCAGCC AGAGATCCGCMutations can be generated in MinD sequences from a variety ofcyanobacterial species, for example, by transforming cells from selectedcyanobacterial species with a targeting vector that includes twoflanking segments, for example, SEQ ID NO:21 and 22 in Synechococcuselongatus and related cyanobacterial species. Such targeting vectors canbe used for cyanobacterial species other than Synechococcus elongatus,for example, by using targeting vectors that have flanking segmentsequences that have less than 100%, or less than 99%, or less than 98%,or less than 95%, or less than 90%, or less than 85%, or less than 75%sequence identity to SEQ ID NO:21 and/or 22. In some cases the targetingvectors that have flanking segment sequences that have at least 70%, orat least 75%, or at least 80%, or at least 85%, or at least 90%, or atleast 95%, or at least 97%, or at least 98%, or at least 99% sequenceidentity to SEQ ID NOs:21 and 22.

In some cases, to induce expression of MinD protein, a promoter regioncan be used in an expression cassette or vector where the promoter hasat least at least 70%, or at least 75%, or at least 80%, or at least85%, or at least 90%, or at least 95%, or at least 97%, or at least 98%,or at least 99% sequence identity to SEQ ID NO:21 or 22.

MinE

MinE proteins are antagonists of MinC proteins, so cells withloss-of-function mutations of MinE cells are longer than wild typecyanobacterial cells of the same species. One sequence for aSynechococcus elongatus MinE polypeptide has the following sequence (SEQID NO:23).

1 MLADLFERLF PRQQASRDTV KQRLKLVLAH DRADLSPELL 41QKMRQEILEV VSRYVELDSE GMELSLENDQ RVTALVANLP 81 IRRVKPATAE GA nucleic acid that encodes the polypeptide with SEQ ID NO:23 has thesequence shown below as SEQ ID NO:24.

1 ATGCTGGCTG ACTTATTCGA GCGCTTGTTC CCCCGGCAAC 41AGGCCAGTCG AGACACCGTG AAGCAGCGCC TTAAGCTTGT 81GCTGGCTCAC GATCGTGCTG ACCTCAGCCC TGAGCTGTTG 121CAAAAGATGC GCCAAGAGAT TTTAGAAGTG GTCTCTCGCT 161ACGTTGAGCT GGACTCTGAG GGAATGGAAC TCTCGCTAGA 201AAATGACCAG CGAGTCACAG CACTTGTCGC CAATTTACCG 241ATTCGTCGTG TCAAACCCGC AACTGCTGAA GGATGA

Other cyanobacterial polypeptides and nucleic acids are available withsignificant sequence homology to the SEQ ID NO:23 MinE protein. Forexample, a related Synechococcus sp. PCC 6312 MinE sequence withaccession number WP_015125088.1 (GI:504937986) is available from theNational Center for Biotechnology Information database (see website atncbi.nlm.nih.gov). The sequence for this MinE polypeptide shares 72% ormore sequence identity with SEQ ID NO:23 and is shown below as SEQ IDNO:25.

1 MITDLLERIF PRQQTSRQQV KQRLKLVLAH DRCDLNPEIL 41EHLRQDILEV VSRYVELDLD ALDFSLESDQ RTTALIANLP 81IRRVKLPTPT EESPVPMQPD GLELA comparison between SEQ ID NO:23 and SEQ ID NO:25 MinE sequences isshown below, with highly conserved amino acids identified. The asterisksbelow the comparison show which amino acids are identical.71.6% identity in 88 residues overlap; Score: 323.0; Gap frequency: 0.0%

Seq23 1 MLADLFERLFPRQQASRDTVKQRLKLVLAHDRADLSPELLQKMRQEILEVVSRYVELDSESeq25 1 MITDLLERIFPRQQTSRQQVKQRLKLVLAHDRCDLNPEILEHLRQDILEVVSRYVELDLD*  ** ** ***** **  ************* ** ** *   ** ************ Seq23 61GMELSLENDQRVTALVANLPIRRVKPAT Seq25 61 ALDFSLESDQRTTALIANLPIRRVKLPT    *** *** *** *********  *

Another MinE sequence from Leptolyngbya sp. O-77 is available from theNCBI database as accession number BAU43948.1 (GI:984538968), which hasat least 71% sequence identity to SEQ ID NO:23, and is shown below asSEQ ID NO:26.

1 MLSELLDRLF PRQPEVSSRE TVKQRLQLVL AHDRTDLPPA 41TIEKMRQEIL EVVSRYVEID QEGTEFMLEN NQRATALIAN 81 LPIRRIKSDVA comparison between SEQ ID NO:23 and SEQ ID NO:26 MinE sequences isshown below, with highly conserved amino acids identified. The asterisksbelow the comparison show which amino acids are identical.71.3% identity in 87 residues overlap; Score: 301.0; Gap frequency: 2.3%

Seq23 1 MLADLFERLFPRQQ--ASRDTVKQRLKLVLAHDRADLSPELLQKMRQEILEVVSRYVELDSeq26 1 MLSELLDRLFPRQPEVSSRETVKQRLQLVLAHDRTDLPPATIEKMRQEILEVVSRYVEID**  *  ******    ** ****** ******* ** *    *************** * Seq23 59SEGMELSLENDQRVTALVANLPIRRVK Seq26 61 QEGTEFMLENNQRATALIANLPIRRIK ** *  *** ** *** ******* *

Another MinE sequence from Lyngbya aestuarii is available from the NCBIdatabase as accession number WP_040483865.1 (GI:750179791), which has atleast 73% sequence identity to SEQ ID NO:23, and is shown below as SEQID NO:27.

1 MKLNELLERL FPRSTNSRED VKRRLKLVLA HDRADLTPEL 41IEAMRQEILE VLSRYVEIDT EDSEFGLESD QRATALIANL 81 PIRRVKNTPD VNQTSPTSPD APLA comparison between SEQ ID NO:23 and SEQ ID NO:27 MinE sequences isshown below, with highly conserved amino acids identified. The asterisksbelow the comparison show which amino acids are identical.72.6% identity in 84 residues overlap; Score: 306.0; Gap frequency: 0.0%

Seq23 2 LADLFERLFPRQQASRDTVKQRLKLVLAHDRADLSPELLQKMRQEILEVVSRYVELDSEGSeq27 3 LNELLERLFPRSTNSREDVKRRLKLVLAHDRADLTPELIEAMRQEILEVLSRYVEIDTED*  * ******   **  ** ************* ***   ******** ***** * * Seq23 62MELSLENDQRVTALVANLPIRRVK Seq27 63 SEFGLESDQRATALIANLPIRRVK *  ** *** *** *********

Another MinE sequence from Calothrix sp. PCC 7103 is available from theNCBI database as accession number WP_040483865.1 (GI:750179791), whichhas at least 64% sequence identity to SEQ ID NO:23, and is shown belowas SEQ ID NO:28.

1 MILEFIERLF SRSNDTSRSE VKRRLQLVIA HDRADLSPQM 41IEKMRQEILE IVCRYVEVET EGLEFSLESN QRTTALIANL 81 PIRRVKESTS EEEANSEKVA comparison between SEQ ID NO:23 and SEQ ID NO:28 MinE sequences isshown below, with highly conserved amino acids identified. The asterisksbelow the comparison show which amino acids are identical.63.7% identity in 91 residues overlap; Score: 293.0; Gap frequency: 1.1%

Seq23 1 MLADLFERLFPRQQ-ASRDTVKQRLKLVLAHDRADLSPELLQKMRQEILEVVSRYVELDSSeq28 1 MILEFIERLFSRSNDTSRSEVKRRLQLVIAHDRADLSPQMIEKMRQEILEIVCRYVEVET*     **** *    **  ** ** ** *********    ******** * **** Seq23 60EGMELSLENDQRVTALVANLPIRRVKPATAE Seq28 61 EGLEFSLESNQRTTALIANLPIRRVKESTSE** * ***  ** *** *********  * *

Another MinE sequence from Leptolyngbya sp. Heron Island J is availablefrom the NCBI database as accession number WP_023071655.1(GI:553737423), which has at least 71% sequence identity to SEQ IDNO:23, and is shown below as SEQ ID NO:29.

1 MISDFFERLF GSREPVSRDT AKQRLRFVLA HDRSDISPQN 41LEKLRQEILE VVSRYVELDF DGLEFSLESD QRMTALMANL 61PIRRVRSNPL EPDSPVEETE AKNLELTDES IALDDEVEEV 121 SETADIPLDA comparison between SEQ ID NO:23 and SEQ ID NO:29 MinE sequences isshown below, with highly conserved amino acids identified. The asterisksbelow the comparison show which amino acids are identical.70.9% identity in 86 residues overlap; Score: 303.0; Gap frequency: 1.2%

Seq23 1 MLADLFERLF-PRQQASRDTVKQRLKLVLAHDRADLSPELLQKMRQEILEVVSRYVELDSSeq29 1 MISDFFERLFGSREPVSRDTAKQRLRFVLAHDRSDISPQNLEKLRQEILEVVSRYVELDF*  * *****  *   **** ****  ****** * **  * * *************** Seq23 60EGMELSLENDQRVTALVANLPIRRVK Seq29 61 DGLEFSLESDQRMTALMANLPIRRVR * * *** *** *** ********

Another MinE sequence from Scytonema millei is available from the NCBIdatabase as accession number WP_039717520.1 (GI:748142306), which has atleast 67% sequence identity to SEQ ID NO:23, and is shown below as SEQID NO:30.

1 MFSDLFDKIF SSNPNDNNSR SQVKQRLQLV ISHDRSDLSP 41QTIEKMRREI LEVVGRYVEL DVEGMEFSLE NNQRATALIA 81 NLPIRRVKTD EA comparison between SEQ ID NO:23 and SEQ ID NO:30 MinE sequences isshown below, with highly conserved amino acids identified. The asterisksbelow the comparison show which amino acids are identical.67.0% identity in 88 residues overlap; Score: 286.0; Gap frequency: 3.4%

Seq23 1 MLADLFERLF---PRQQASRDTVKQRLKLVLAHDRADLSPELLQKMRQEILEVVSRYVELSeq30 1 MFSDLFDKIFSSNPNDNNSRSQVKQRLQLVISHDRSDLSPQTIEKMRREILEVVGRYVEL*  ***   *   *    **  ***** **  *** ****    *** ****** ***** Seq23 58DSEGMELSLENDQRVTALVANLPIRRVK Seq30 61 DVEGMEFSLENNQRATALIANLPIRRVK* **** **** ** *** *********

Another MinE sequence from Microcoleus sp. PCC 7113 is available fromthe NCBI database as accession number WP_015183206.1 (GI:504996104),which has at least 64% sequence identity to SEQ ID NO:23, and is shownbelow as SEQ ID NO:31.

1 MISDLLERLF PWTSASNSRA EVKRRLQLVI AHDRADLTPQ 41MIEKMRNEIL EVVSRYVEIE TEGLEIALES NQRVTALIAN 81LPIRRVKEEA PVASGGVEPG IDLIGA comparison between SEQ ID NO:23 and SEQ ID NO:31 MinE sequences isshown below, with highly conserved amino acids identified. The asterisksbelow the comparison show which amino acids are identical.67.8% identity in 87 residues overlap; Score: 291.0; Gap frequency: 2.3%

Seq23 1 MLADLFERLFPRQQAS--RDTVKQRLKLVLAHDRADLSPELLQKMRQEILEVVSRYVELDSeq31 1 MISDLLERLFPWTSASNSRAEVKRRLQLVIAHDRADLTPQMIEKMRNEILEVVSRYVEIE*  ** *****   **  *  ** ** ** ******* *    *** *********** Seq23 59SEGMELSLENDQRVTALVANLPIRRVK Seq31 61 TEGLEIALESNQRVTALIANLPIRRVK ** *  **  ****** *********

Another MinE-like sequence from Synechococcus elongatus PCC 7942 isavailable from the NCBI database as accession number AAA16171.1(GI:310860), is shown below as SEQ ID NO:32.

1 MTQAQSLDVL NLLEQLEESV LDGTRVPLSG RILVRENDLL 41DLLDDVRAGL PAAIQQAQQI LERQAQILAD AQQQAQAIVA 81QAQQERALLI DQNSIRLQAE RDASSSAKPF NRNVMPFGNR 121RSRKQHKCGA RPNSSSSKSA RKPTVFASRP KPKSSSCAAK 161LNSSYLSSAK GFWSNVRSCG GVLTAMLTKF CGTWSSD

Any of the Min proteins and/or their related proteins, for example withconserved domains illustrated by the sequence comparisons shown above,can be expressed in cells (e.g., via a transgene or expression cassetteintroduced into a host cell) to increase the activity of the MinEproteins described herein.

As illustrated in FIG. 2C, deletion or inactivation of MinE tends toelongate cells while overexpression of MinE does not. For example, themean cell length of inactivated MinE mutants can be at least 150%, or atleast 200%, or at least 250%, or at least 300%, or at least 500%, or atleast 750%, or at least 1000%, or at least 5000%, or at least 10000%, orat least 15000%, or at least 20000% greater than a wild type populationof cyanobacteria of the same species.

Complete deletion of an endogenous MinE gene may be lethal. Hence,partial deletion or inactivation of MinE function may be a betterapproach.

For example, MinE mutations can be introduced to increase cell size bymethods that can include partial deletion or insertion of foreign DNAinto the MinE locus. For example, this can involve the use of eithertransposable elements or T-DNA. The foreign DNA not only disrupts theexpression of the gene into which it is inserted but also acts as amarker for subsequent identification of the mutation. If a large enoughpopulation of transposon-transformed or T-DNA-transformed lines isavailable, one has a very good chance of finding a cyanobacteriacarrying an insertion within any gene of interest.

Any of the conserved amino acids and conserved domains illustrated bythe sequence comparisons shown above can be deleted or mutated to reducethe activity of the MinE proteins described herein and thereby increasecell size. For example, to increase cyanobacterial cell sizes apopulation of cyanobacteria can include a mutation of any of SEQ IDNOs:23, 25-31, or 32.

A wild type cyanobacterial population can have a MinE polypeptide withat least 70%, or at least 75%, or at least 80%, or at least 85%, or atleast 90%, or at least 95%, or at least 97%, or at least 98%, or atleast 99% sequence identity to any of SEQ ID NOs:23, 25-31, or 32.

However, the cyanobacterial strain with increased cell length canexpress mutant MinE polypeptides that have reduced MinE activity. SuchMinE polypeptides that have reduced MinE activity can have less than99%, or less than 98%, or less than 95%, or less than 90%, or less than85%, or less than 75%, or less than 60%, or less than 50%, or less than40%, or less than 30%, or less than 20% sequence identity to any of SEQID NOs:23, 25-31, or 32. The mutations in mutant MinE polypeptides can,for example, have mutations in at least one conserved amino acidposition, or at least two conserved amino acid positions, or at leastthree conserved amino acid positions, or at least five conserved aminoacid positions, or at least seven conserved amino acid positions, or atleast eight conserved amino acid positions, or at least ten conservedamino acid positions, or at least fifteen amino acid positions, or atleast twenty conserved amino acid positions, or at least twenty-fiveamino acid positions. In some cases, an entire conserved MinE domain canbe deleted. Alternatively, the endogenous MinE gene is partially deletedor mutated.

The conserved amino acids are in many cases mutated by deletion orreplacement with amino acids that have dissimilar physical and/orchemical properties.

Cdv3 (DivIVA)

Cdv3 proteins promote cell division. Hence, cyanobacterial cells thatexpress increased levels of the Cdv3 or DivIVA protein are larger thanwild type cells with no such Cdv3 or DivIVA overexpression. Cells withloss-of-function Cdv3 or DivIVA mutations are smaller than wild typecyanobacterial cells of the same species.

For example, the mean cell length of Cdv3 overexpressing cyanobacterialcells is at least 150%, or at least 200%, or at least 250%, or at least300%, or at least 500%, or at least 750%, or at least 1000%, or at least5000%, or at least 10000%, or at least 15000%, or at least 20000%greater than a wild type population of cyanobacteria of the samespecies.

One sequence for a Synechococcus elongatus Cdv3 polypeptide has thefollowing sequence (SEQ ID NO:33).

1 MTQAQSLDVL NLLEQLEESV LDGTRVPLSG RILVRENDLL 41DLLDDVRAGL PAAIQQAQQI LERQAQILAD AQQQAQAIVA 81QAQQERALLI DQNSIRLQAE RDAQQLRQTL QQECDALRQQ 121AIAEATQVRG EAQQFQLQVR QETDSLRQQT QAEIEQLRSQ 161TQQQLSEQRQ RILVECEELR RGADSYADQV LRDMEQRLTQ 201MMQIIRNGRQ ALNLSENTPP PAPRRRSRA nucleic acid that encodes the polypeptide with SEQ ID NO:33 has thesequence shown below as SEQ ID NO:34.

1 GTGACCCAAG CCCAATCACT CGATGTCTTG AACTTGCTAG 41AGCAGCTCGA AGAGTCTGTG CTCGACGGGA CTCGCGTGCC 81GCTTTCGGGG CGCATTCTGG TTCGAGAAAA CGACCTGCTC 121GACCTGTTAG ATGACGTGCG TGCCGGGTTG CCCGCTGCGA 161TTCAACAAGC TCAGCAAATC CTCGAGCGCC AAGCCCAAAT 201TTTGGCTGAC GCCCAACAGC AAGCACAGGC GATCGTGGCG 241CAGGCGCAGC AAGAACGGGC CCTGCTGATT GACCAAAACA 281GTATTCGGCT TCAAGCTGAG CGCGATGCGC AGCAGCTCCG 321CCAAACCCTT CAACAGGAAT GTGATGCCCT TCGGCAACAG 361GCGATCGCGG AAGCAACACA AGTGCGGGGC GAGGCCCAAC 401AGTTCCAGCT CCAAGTCCGC CAGGAAACCG ACAGTCTTCG 441CCAGCAGACC CAAGCCGAAA TCGAGCAGCT GCGCAGCCAA 481ACTCAACAGC AGCTATCTGA GCAGCGCCAA AGGATTTTGG 521TCGAATGTGA GGAGTTGCGG CGGGGTGCTG ACAGCTATGC 561TGACCAAGTT CTGCGGGACA TGGAGCAGCG ATTGACCCAG 601ATGATGCAGA TCATCCGCAA TGGTCGTCAG GCCCTGAACT 641TGAGCGAAAA TACGCCGCCC CCTGCTCCCC GTCGGCGATC 681 GCGCTAA

Other cyanobacterial polypeptides and nucleic acids are available withsignificant sequence homology to the SEQ ID NO:33 Cdv3 protein. Forexample, a related Leptolyngbya sp. Heron Island J Cdv3 sequence withaccession number WP_023073979.1 (GI:553739790) is available from theNational Center for Biotechnology Information database (see website atncbi.nlm.nih.gov). The sequence for this Cdv3 polypeptide shares 41% ormore sequence identity with SEQ ID NO:33 and is shown below as SEQ IDNO:35.

1 MVRQEPPIND PRLINDPRLN GQVDDVLAQQ QIGNVTPGPV 41AGFDIQDALN QIEEAVLDSP RLPVMGRTMI NEDDLLDQLD 61AVRLNLPGAF QEAQQLLEQR DDILSEAERY AQDIVTTAEK 121QAAAILNETT ILRQAEQQAQ QLRLQVEQEC AALRSQTMME 161IEQLQAQTNQ ECDEMRKSAI TECHAIQTDA DTYADQVLQR 201METQFSEMLD VISNGRQQLY ERQQRARQTA PTPPSSASSG 241DVPVAPLSRR PISQRPPGQQ SYIQPPPSTP PSRPQQQPPR 281 PQQPPRPQQR PPRKFA comparison between SEQ ID NO:33 and SEQ ID NO:35 Cdv3 sequences isshown below, with highly conserved amino acids identified. The asterisksbelow the comparison show which amino acids are identical.41.5% identity in 205 residues overlap; Score: 313.0; Gap frequency:14.1%

Seq33 8 DVLNLLEQLEESVLDGTRVPLSGRILVRENDLLDLLDDVRAGLPAAIQQAQQILERQAQISeq35 44 DIQDALNQIEEAVLDSPRLPVMGRTMINEDDLLDQLDAVRLNLPGAFQEAQQLLEQRDDI*    * * ** ***  * *  **    * **** ** **  ** * * *** **    * Seq33 68LADAQQQAQAIVAQAQQERALLIDQNSIRLQAERDAQQLRQTLQQECDALRQQAIAEATQ Seq35 104LSEAERYAQDIVTTAEKQAAAILNETTILRQAEQQAQQLRLQVEQECAALRSQ-------*  *   ** **  *    *       *  ***  *****    *** *** * Seq33 128VRGEAQQFQLQVRQETDSLRQQTQAEIEQLRSQTQQQLSEQRQRILVECEELRRGADSYA Seq35 157----------------------TMMEIEQLQAQTNQECDEMRKSAITECHAIQTDADTYA                      *  *****  ** *   * *     **      ** ** Seq33 188DQVLRDMEQRLTQMMQIIRNGRQAL Seq35 195 DQVLQRMETQFSEMLDVISNGRQQL****  **     *   * **** *

Another Cdv3 sequence from Leptolyngbya sp. PCC 7375 is available fromthe NCBI database as accession number WP_006517434.1 (GI:493564058),which has at least 42% sequence identity to SEQ ID NO:33, and is shownbelow as SEQ ID NO:36.

1 MVRQEPPLND PRLVNDPRLV NDPRLNGQAA QVDDVLAQQQ 41IGKAGPAPMA GFDIQDALNQ IEESVLDSPR LPVMGRTMIN 81EDDLLDQLDA VRLNLPSAFQ EAQQLVEQRD DILNEAERYA 121QNIVTAAEKQ AATILNETSI LRQAEQQAQQ LRLQVEQECA 161ALRSQTMLEI EQLQTQTKQE CEDLRQNAIA ECHAIQTDAD 201TYADQVLQRM ETQFSEMLGV ISNGRQQLYE RQQRARQTAP 241PSMPAASDVV APPNPLNRCP ATQRPSSTQQ SYIQPPQQQP 281PTRSPQQQPP TRPPQQPPRP QQRPPRKFA comparison between SEQ ID NO:33 and SEQ ID NO:36 Cdv3 sequences isshown below, with highly conserved amino acids identified. The asterisksbelow the comparison show which amino acids are identical.42.0% identity in 205 residues overlap; Score: 313.0; Gap frequency:14.1%

Seq33 8 DVLNLLEQLEESVLDGTRVPLSGRILVRENDLLDLLDDVRAGLPAAIQQAQQILERQAQISeq36 53 DIQDALNQIEESVLDSPRLPVMGRTMINEDDLLDQLDAVRLNLPSAFQEAQQLVEQRDDI*    * * ******  * *  **    * **** ** **  ** * * ***  *    * Seq33 68LADAQQQAQAIVAQAQQERALLIDQNSIRLQAERDAQQLRQTLQQECDALRQQAIAEATQ Seq36 113LNEAERYAQNIVTAAEKQAATILNETSILRQAEQQAQQLRLQVEQECAALRSQ-------*  *   ** **  *    *      **  ***  *****    *** *** * Seq33 128VRGEAQQFQLQVRQETDSLRQQTQAEIEQLRSQTQQQLSEQRQRILVECEELRRGADSYA Seq36 166----------------------TMLEIEQLQTQTKQECEDLRQNAIAECHAIQTDADTYA                      *  *****  ** *     **    **      ** ** Seq33 188DQVLRDMEQRLTQMMQIIRNGRQAL Seq36 204 DQVLQRMETQFSEMLGVISNGRQQL****  **     *   * **** *

Another Cdv3 sequence from Neosynechococcus sphagnicola sy1 is availablefrom the NCBI database as accession number KGF72132.1 (GI:691246400),which has at least 40% sequence identity to SEQ ID NO:33, and is shownbelow as SEQ ID NO:37.

1 MQHPAEALDV QRELNKLEEM ILDSPRLPFS GRTLVDEEHI 41LDQVDLIRLS LPAAFHEAEE MVRRKDELLS QAEHYAQERI 61DQAERQAAQI LDEIGIIQQA EQEARQIRQR VQQECEAAQT 121HTMAEIERMH RQAQQELEEM RRLAISECHD IQHEADVYAD 161RVLKSMEQQL GEMMRVIRNG RQQLQPEPPP SRREQREDGT 201TTNPGRPTPP AVHTQTQTRM PERIKGA comparison between SEQ ID NO:33 and SEQ ID NO:37 Cdv3 sequences isshown below, with highly conserved amino acids identified. The asterisksbelow the comparison show which amino acids are identical.38.6% identity in 223 residues overlap; Score: 297.0; Gap frequency:14.3%

Seq33 4 AQSLDVLNLLEQLEESVLDGTRVPLSGRILVRENDLLDLLDDVRAGLPAAIQQAQQILERSeq37 5 AEALDVQRELNKLEEMILDSPRLPFSGRTLVDEEHILDQVDLIRLSLPAAFHEAEEMVRR*  ***   *  ***  **  * * *** ** *   **  *  *  ****   *     * Seq33 64QAQILADAQQQAQAIVAQAQQERALLIDQNSIRLQAERDAQQLRQTLQQECDALRQQAIA Seq37 65KDELLSQAEHYAQERIDQAERQAAQILDEIGIIQQAEQEARQIRQRVQQECEAAQTH---    *  *   **    **    *   *   *  ***  * * **  **** * Seq33 124EATQVRGEAQQFQLQVRQETDSLRQQTQAEIEQLRSQTQQQLSEQRQRILVECEELRRGA Seq37 122--------------------------TMAEIERMHRQAQQELEEMRRLAISECHDIQHEA                          * ****    * ** * * *     **      * Seq33 184DSYADQVLRDMEQRLTQMMQIIRNGRQALNLSENTPPPAPRRR Seq37 156DVYADRVLKSMEQQLGEMMRVIRNGRQQL---QPEPPPSRREQ* *** **  *** *  **  ****** *      ***  *

Another Cdv3 sequence from Planktothrix is available from the NCBIdatabase as accession number WP_026787539.1 (GI:652391691), which has atleast 40% sequence identity to SEQ ID NO:33, and is shown below as SEQID NO:38.

1 MLRQESTPRL EPEQNGLRVE PETTVSNSPG IDIQRELNRL 41EEMILDSPRI PLTRRTLVDE EQLLDQLDLI RLNLPSAFQE 81SDIIVRHKDE ILQEAEEYAQ EIVTMAEQRA ARILNEMGLI 121QQAKSEADQL RQQVQNECDT LQQQTLSEIE QIRYRLQQEL 161EEMRSRTMAE CEEIQNGADD YADHVLGSIE QQLNEMMRVI 181 RNGRQQVQGN NPTRA comparison between SEQ ID NO:33 and SEQ ID NO:38 Cdv3 sequences isshown below, with highly conserved amino acids identified. The asterisksbelow the comparison show which amino acids are identical.40.0% identity in 210 residues overlap; Score: 305.0; Gap frequency:13.8%

Seq33 1 MTQAQSLDVLNLLEQLEESVLDGTRVPLSGRILVRENDLLDLLDDVRAGLPAAIQQAQQISeq38 25 VSNSPGIDIQRELNRLEEMILDSPRIPLTRRTLVDEEQLLDQLDLIRLNLPSAFQESDII       *    *  ***  **  * **  * ** *  *** **  *  ** * *    * Seq33 61LERQAQILADAQQQAQAIVAQAQQERALLIDQNSIRLQAERDAQQLRQTLQQECDALRQQ Seq38 85VRHKDEILQEAEEYAQEIVTMAEQRAARILNEMGLIQQAKSEADQLRQQVQNECD-----      **  *   ** **  * *  *          **   * ****  * *** Seq33 121AIAEATQVRGEAQQFQLQVRQETDSLRQQTQAEIEQLRSQTQQQLSEQRQRILVECEELR Seq38 140------------------------TLQQQTLSEIEQIRYRLQQELEEMRSRTMAECEEIQ                         * ***  **** *   ** * * * *   **** Seq33 181RGADSYADQVLRDMEQRLTQMMQIIRNGRQ Seq38 176 NGADDYADHVLGSIEQQLNEMMRVIRNGRQ *** *** **   ** *  **  ******

Another Cdv3 sequence from Geitlerinema sp. PCC 7105 is available fromthe NCBI database as accession number WP_017658745.1 (GI:516254782),which has at least 40% sequence identity to SEQ ID NO:33, and is shownbelow as SEQ ID NO:39.

1 MLRQDSAGID PKSDSPQPQG EPAQTVAPEQ RQEGANQGSV 41 NVQQALNRLE EAILDSPRIPFTGRTLVDEE PLLDILDAIR 81 LNLPAAFQEA EEVIRQKDEI LRQAEQYGRE IVDAAEQQAA 121SILDEMGLVR QAKVEADRLR QQVQADCEVA RERAISEIEQ 161 MQRQAQQELE EVRARALAEAEQIEAGADEY ADRVLRNIEQ 201 QLSDMMRVIR NGRQQLQQEV AYRAHQKEPK VNPNVRRYA comparison between SEQ ID NO:33 and SEQ ID NO:39 Cdv3 sequences isshown below, with highly conserved amino acids identified. The asterisksbelow the comparison show which amino acids are identical.40.1% identity in 207 residues overlap; Score: 306.0; Gap frequency:14.0%

Seq33 6 SLDVLNLLEQLEESVLDGTRVPLSGRILVRENDLLDLLDDVRAGLPAAIQQAQQILERQASeq39 39 SVNVQQALNRLEEAILDSPRIPFTGRTLVDEEPLLDILDAIRLNLPAAFQEAEEVIRQKD*  *   *  ***  **  * *  ** ** *  *** **  *  **** * * Seq33 66QILADAQQQAQAIVAQAQQERALLIDQNSIRLQAERDAQQLRQTLQQECDALRQQAIAEA Seq39 99EILRQAEQYGREIVDAAEQQAASILDEMGLVRQAKVEADRLRQQVQADCEVARERAISE-  **  **    **  * *  *   *      **   *  ***  *  *   *  ** * Seq33 126TQVRGEAQQFQLQVRQETDSLRQQTQAEIEQLRSQTQQQLSEQRQRILVECEELRRGADS Seq39 158----------------------------IEQMQRQAQQELEEVRARALAEAEQIEAGADE                            ***   * ** * * * * * * *    *** Seq33 186YADQVLRDMEQRLTQMMQIIRNGRQAL Seq39 190 YADRVLRNIEQQLSDMMRVIRNGRQQL ******  ** *  **  ****** *

Any of the conserved amino acids and conserved domains illustrated bythe sequence comparisons shown above can be expressed in cells (e.g.,via a transgene or expression cassette introduced into a host cell) toincrease the activity of the Cdv3 proteins described herein.

As illustrated in FIGS. 2C-2D, 2F, overexpression of Cdv3 tends toelongate cells. To increase cyanobacterial cell sizes a population ofcyanobacteria can include an expression cassette or vector that encodesa Cdv3 polypeptide. For example, an expression cassette or vector thatencodes can include a Cdv3 polypeptide with at least 70%, or at least75%, or at least 80%, or at least 85%, or at least 90%, or at least 95%,or at least 97%, or at least 98%, or at least 99% sequence identity toany of SEQ ID NOs:33, 35-38, or 39.

Any of the conserved amino acids and conserved domains illustrated bythe sequence comparisons shown above can be deleted in cells to reducethe expression and/or activity of the (e.g., endogenous) Cdv3 proteinsdescribed herein. As illustrated in FIG. 2C deletion of Cdv3 can alsolead to elongation of cells.

For example, Cdv3 mutations can be introduced to increase cell size bymethods that can include deletion of Cdv3 sequences or insertion offoreign DNA into the Cdv3 locus. For example, this can involve the useof either transposable elements or T-DNA. The foreign DNA not onlydisrupts the expression of the gene into which it is inserted but alsoacts as a marker for subsequent identification of the mutation. If alarge enough population of transposon-transformed or T-DNA-transformedlines is available, one has a very good chance of finding acyanobacteria carrying an insertion within any gene of interest.

Any of the conserved amino acids and conserved domains illustrated bythe sequence comparisons shown above can be deleted or mutated to reducethe activity of the Cdv3 proteins described herein and thereby increasecell size. For example, to increase cyanobacterial cell sizes apopulation of cyanobacteria can include a mutation of any of SEQ IDNOs:33, 35-38, or 39.

A wild type cyanobacterial population can have a Cdv3 polypeptide withat least 70%, or at least 75%, or at least 80%, or at least 85%, or atleast 90%, or at least 95%, or at least 97%, or at least 98%, or atleast 99% sequence identity to any of SEQ ID NOs:33, 25-38, or 39.

However, the cyanobacterial strain with increased cell length canexpress mutant Cdv3 polypeptides that have reduced Cdv3 activity. SuchCdv3 polypeptides that have reduced Cdv3 activity can have less than99%, or less than 98%, or less than 95%, or less than 90%, or less than85%, or less than 75%, or less than 60%, or less than 50%, or less than40%, or less than 30%, or less than 20% sequence identity to any of SEQID NOs:33, 35-38, or 39. The mutations in mutant Cdv3 polypeptides can,for example, have mutations in at least one conserved amino acidposition, or at least two conserved amino acid positions, or at leastthree conserved amino acid positions, or at least five conserved aminoacid positions, or at least seven conserved amino acid positions, or atleast eight conserved amino acid positions, or at least ten conservedamino acid positions, or at least fifteen amino acid positions, or atleast twenty conserved amino acid positions, or at least twenty-fiveamino acid positions. In some cases, an entire conserved Cdv3 domain orthe entire endogenous Cdv3 gene is deleted or mutated.

The conserved amino acids are in many cases mutated by deletion orreplacement with amino acids that have dissimilar physical and/orchemical properties.

FtsZ Sequences

FtsZ proteins polymerize or self-assemble to form a contractile “Z ring”(usually in the middle of the cell) that mediates actual cell division.The Min proteins modulate the self-assembly or positioning of FtsZrings.

In some cases, cyanobacterial cells that express increased levels of theFtsZ protein can be smaller than wild type cells with no such FtsZoverexpression. Cells with loss-of-function FtsZ mutations can in somecases be larger than wild type cyanobacterial cells of the same species.

One example of a Synechococcus elongatus 7942 FtsZ protein sequence isshown below as SEQ ID NO:40.

1 MTDPMPINNS YGFNRDGSLS GFDALGQPEE LIIPSSVARI 41 KVIGVGGGGS NGVNRMISSDVSGVEFWALN TDAQALLHSA 81 APKRMQLGQK LTRGLGAGGN PAIGMKAAEE SREELIAALE 121GADLVFITAG MGGGTGTGAA PIVAEVAKEV GALTVGIVTK 161 PFTFEGRRRM KQAEEGTAALQSSVDTLITI PNDRLLHAIS 201 EQTPIQEAFR VADDILRQGV QGISDIITIP GLVNVDFADV241 RAVMADAGSA LMGIGSGSGK SRAREAAHAA ISSPLLESSI 281 EGARGVVFNITGGRDMTLHE VNAAADAIYE VVDPEANIIF 321 GAVIDDRLEG ELRITVIATG FSTDRPNLNTISTSTSQPTS 361 QPSVSPNPAS APPASGGGLD IPAFLQRKIQ NRPA nucleotide sequence encoding the Synechococcus elongatus 7942 SEQ IDNO:40 FtsZ protein is shown below (SEQ ID NO:41).

1 ATGACCGACC CTATGCCGAT CAACAATTCC TATGGCTTCA 41 ACCGTGACGG CTCTCTGTCGGGGTTCGATG CACTAGGGCA 81 GCCAGAAGAA CTAATCATCC CCAGCAGCGT TGCCCGCATC 121AAAGTAATTG GCGTTGGCGG TGGCGGCAGC AACGGGGTCA 161 ACCGCATGAT TAGCAGCGATGTCAGCGGGG TTGAATTTTG 201 GGCCCTCAAC ACTGATGCTC AAGCTTTGCT CCACTCTGCA241 GCCCCCAAGC GGATGCAGTT GGGACAGAAA CTAACGCGAG 281 GGCTAGGCGCAGGTGGCAAC CCTGCGATCG GCATGAAAGC 321 CGCTGAAGAA TCGCGGGAAG AACTAATCGCCGCCTTGGAA 361 GGGGCTGACC TCGTCTTTAT CACGGCGGGG ATGGGCGGTG 401GAACCGGCAC TGGAGCTGCC CCGATCGTGG CAGAAGTCGC 441 CAAAGAAGTG GGTGCGCTGACGGTTGGGAT TGTCACCAAA 481 CCCTTCACCT TCGAAGGGCG TCGCCGAATG AAGCAGGCGG521 AAGAAGGAAC AGCCGCACTG CAAAGCTCAG TCGACACTTT 561 GATCACTATTCCTAATGACC GCCTACTCCA CGCCATATCT 601 GAGCAGACGC CGATTCAAGA AGCTTTCCGGGTCGCCGACG 641 ATATTCTCCG GCAGGGTGTG CAAGGGATTT CTGACATCAT 681CACGATCCCA GGTCTGGTCA ACGTCGACTT TGCCGACGTT 721 CGCGCCGTCA TGGCCGATGCTGGATCAGCC CTGATGGGCA 761 TCGGTAGCGG CTCTGGCAAG TCCCGCGCTC GGGAAGCCGC801 TCATGCAGCC ATTAGCTCAC CGCTGCTGGA GTCTTCGATC 841 GAAGGGGCGCGCGGCGTTGT CTTCAACATC ACAGGCGGCC 881 GCGATATGAC CCTGCATGAG GTCAACGCAGCAGCGGATGC 921 GATTTACGAA GTCGTCGATC CTGAAGCCAA TATCATTTTC 961GGCGCCGTGA TTGACGATCG ATTGGAAGGA GAGCTGCGGA 1001 TCACCGTGAT CGCCACGGGCTTCAGCACCG ATCGCCCCAA 1041 CCTCAACACG ATTTCCACCA GCACGTCCCA GCCGACCAGC1081 CAACCCAGCG TGAGTCCCAA CCCAGCTAGT GCCCCACCGG 1121 CGAGCGGCGGCGGCCTCGAC ATTCCGGCCT TCCTACAACG 1161 GAAAATTCAA AACCGACCCT AG

Other polypeptides and nucleic acids are available with significantsequence homology to the SEQ ID NO:40 FtsZ protein. For example, arelated Escherichia coli str. K-12 substr. MG1655 sequence is availableas SEQ ID NO:42, shown below.

1 MFEPMELTND AVIKVIGVGG GGGNAVEHMV RERIEGVEFF 41 AVNTDAQALR KTAVGQTIQIGSGITKGLGA GANPEVGRNA 61 ADEDRDALRA ALEGADMVFI AAGMGGGTGT GAAPVVAEVA 121KDLGILTVAV VTKPFNFEGK KRMAFAEQGI TELSKHVDSL 161 ITIPNDKLLK VLGRGISLLDAFGAANDVLK GAVQGIAELI 201 TRPGLMNVDF ADVRTVMSEM GYAMMGSGVA SGEDRAEEAA241 EMAISSPLLE DIDLSGARGV LVNITAGFDL RLDEFETVGN 281 TIRAFASDNATVVIGTSLDP DMNDELRVTV VATGIGMDKR 321 PEITLVTNKQ VQQPVMDRYQ QHGMAPLTQEQKPVAKVVND 361 NAPQTAKEPD YLDIPAFLRK QAD

The sequence for this SEQ ID NO:42 FtsZ polypeptide shares 54% or moresequence identity with SEQ ID NO:40 as illustrated below. The asterisksbelow the comparison show which amino acids are identical.

54.1% identity in 318 residues overlap; Score: 852.0; Gap frequency:0.3%

Seq40 38 ARIKVIGVGGGGSNGVNRMISSDVSGVEFWALNTDAQALLHSAAPKRMQLGQKLTRGLGASeq42 11 AVIKVIGVGGGGGNAVEHMVRERIEGVEFFAVNTDAQALRKTAVGQTIQIGSGITKGLGA *********** * *  *      **** * *******   *     * *   * **** Seq40 98GGNPAIGMKAAEESREELIAALEGADLVFITAGMGGGTGTGAAPIVAEVAKEVGALTVGI Seq42 71GANPEVGRNAADEDRDALRAALEGADMVFIAAGMGGGTGTGAAPVVAEVAKDLGILTVAV ***  *  ** * *  * ******* *** ************* ******  * *** Seq40 158VTKPFTFEGRRRMKQAEEGTAALQSSVDTLITIPNDRLLHAISEQTPIQEAFRVADDILR Seq42 131VTKPFNFEGKKRMAFAEQGITELSKHVDSLITIPNDKLLKVLGRGISLLDAFGAANDVLK ********  **  ** *   *   ** ******* **           **  * * * Seq40 218QGVQGISDIITIPGLVNVDFADVRAVMADAGSALMGIGSGSGKSRAREAAHAAISSPLLE Seq42 191GAVQGIAELITRPGLMNVDFADVRTVMSEMGYAMMGSGVASGEDRAEEAAEMAISSPLLE   ****   ***** ******** **   * * ** *  **  ** ***  ******** Seq40 278S-SIEGARGVVFNITGGRDMTLHEVNAAADAIYEVVDPEANIIFGAVIDDRLEGELRITV Seq42 251DIDLSGARGVLVNITAGFDLRLDEFETVGNTIRAFASDNATVVIGTSLDPDMNDELRVTV          *****  *** * *  * *       *       *    *   *     *** ** Seq40337 IATGFSTDRPNLNTISTS Seq42 311 VATGIGMDKRPEITLVTN  ***   *     *  *A nucleotide sequence encoding the SEQ ID NO:42 protein is shown belowas SEQ ID NO:43.

1 ATGTTTGAAC CAATGGAACT TACCAATGAC GCGGTGATTA 41 AAGTCATCGG CGTCGGCGGCGGCGGCGGTA ATGCTGTTGA 81 ACACATGGTG CGCGAGCGCA TTGAAGGTGT TGAATTCTTC 121GCGGTAAATA CCGATGCACA AGCGCTGCGT AAAACAGCGG 161 TTGGACAGAC GATTCAAATCGGTAGCGGTA TCACCAAAGG 201 ACTGGGCGCT GGCGCTAATC CAGAAGTTGG CCGCAATGCG241 GCTGATGAGG ATCGCGATGC ATTGCGTGCG GCGCTGGAAG 281 GTGCAGACATGGTCTTTATT GCTGCGGGTA TGGGTGGTGG 321 TACCGGTACA GGTGCAGCAC CAGTCGTCGCTGAAGTGGCA 361 AAAGATTTGG GTATCCTGAC CGTTGCTGTC GTCACTAAGC 401CTTTCAACTT TGAAGGCAAG AAGCGTATGG CATTCGCGGA 441 GCAGGGGATC ACTGAACTGTCCAAGCATGT GGACTCTCTG 481 ATCACTATCC CGAACGACAA ACTGCTGAAA GTTCTGGGCC521 GCGGTATCTC CCTGCTGGAT GCGTTTGGCG CAGCGAACGA 561 TGTACTGAAAGGCGCTGTGC AAGGTATCGC TGAACTGATT 601 ACTCGTCCGG GTTTGATGAA CGTGGACTTTGCAGACGTAC 641 GCACCGTAAT GTCTGAGATG GGCTACGCAA TGATGGGTTC 681TGGCGTGGCG AGCGGTGAAG ACCGTGCGGA AGAAGCTGCT 721 GAAATGGCTA TCTCTTCTCCGCTGCTGGAA GATATCGACC 761 TGTCTGGCGC GCGCGGCGTG CTGGTTAACA TCACGGCGGG801 CTTCGACCTG CGTCTGGATG AGTTCGAAAC GGTAGGTAAC 841 ACCATCCGTGCATTTGCTTC CGACAACGCG ACTGTGGTTA 881 TCGGTACTTC TCTTGACCCG GATATGAATGACGAGCTGCG 921 CGTAACCGTT GTTGCGACAG GTATCGGCAT GGACAAACGT 961CCTGAAATCA CTCTGGTGAC CAATAAGCAG GTTCAGCAGC 1001 CAGTGATGGA TCGCTACCAGCAGCATGGGA TGGCTCCGCT 1041 GACCCAGGAG CAGAAGCCGG TTGCTAAAGT CGTGAATGAC1081 AATGCGCCGC AAACTGCGAA AGAGCCGGAT TATCTGGATA 1121 TCCCAGCATTCCTGCGTAAG CAAGCTGATT AA

Another FtsZ sequence from Planktothricoides sp. SR001 is available fromthe NCBI database as accession number WP_054467071.1 (GI:935603347),which has at least 76% sequence identity to SEQ ID NO:40, and is shownbelow as SEQ ID NO:44.

1 MTLNNSLGPV HESPHAQETT SLPPANAENS NPFNNVGLYG 41 GQNLDPIWRE KTPPKEEPRSREIVPSSIAR IKVIGVGGGG 81 CNAVNRMIAS EVSGVEFWGI NTDAQALTQA NAPKRLQIGQ 121KLTRGLGAGG NPAIGQKAAE ESRDEIAAAL DGSDLVFITA 161 GMGGGTGTGA APIVAEAAKEVGALTVGVVT RPFNFEGRRR 201 TSQAEEGIAA LQGRVDTLII IPNDRLLHVI SEQTPVQEAF241 RVADDILRQG VQGISDIITI PGMVNVDFAD VRAIMADAGS 281 ALMGIGTGSGKSRAREAAMA AISSPLMEAS IEGAKGVVFN 321 ITGGGDLTLH EVSAAADIIY EVVDPNANIIFGAVIDERLQ 361 GEIRMTVIAT GFSNEPQPLP QKSRTVPPPP PSFRREASAP 401RTVNPVEPSP QPKPPTQTGG LDIPEFLQRR RPPKA comparison between SEQ ID NO:44 and SEQ ID NO:40 FtsZ sequences isshown below, with highly conserved amino acids identified. The asterisksbelow the comparison show which amino acids are identical.76.6% identity in 368 residues overlap; Score: 1372.0; Gap frequency:3.0%

Seq40 32 IIPSSVARIKVIGVGGGGSNGVNRMISSDVSGVEFWALNTDAQALLHSAAPKRMQLGQKLSeq44 63 IVPSSIARIKVIGVGGGGCNAVNRMIASEVSGVEFWGINTDAQALTQANAPKRLQIGQKL **** ************ * ***** * *******  *******    **** * **** Seq40 92TRGLGAGGNPAIGMKAAEESREELIAALEGADLVFITAGMGGGTGTGAAPIVAEVAKEVG Seq44 123TRGLGAGGNPAIGQKAAEESRDEIAAALDGSDLVFITAGMGGGTGTGAAPIVAEAAKEVG************* ******* *  *** * *********************** ***** Seq40 152ALTVGIVTKPFTFEGRRRMKQAEEGTAALQSSVDTLITIPNDRLLHAISEQTPIQEAFRV Seq44 183ALTVGVVTRPFNFEGRRRTSQAEEGIAALQGRVDTLIIIPNDRLLHVISEQTPVQEAFRV ***** ** ********  ***** ****  ***** ******** ****** ****** Seq40 212ADDILRQGVQGISDIITIPGLVNVDFADVRAVMADAGSALMGIGSGSGKSRAREAAHAAI Seq44 243ADDILRQGVQGISDIITIPGMVNVDFADVRAIMADAGSALMGIGTGSGKSRAREAAMAAI******************** ********** ************ *********** *** Seq40 272SSPLLESSIEGARGVVFNITGGRDMTLHEVNAAADAIYEVVDPEANIIFGAVIDDRLEGE Seq44 303SSPLMEASIEGAKGVVFNITGGGDLTLHEVSAAADIIYEVVDPNANIIFGAVIDERLQGE **** ****** ********* * ***** **** ******* ********** ** ** Seq40 332LRITVIATGFSTDRPNLNTISTST-----------SQPTSQPSVSPNPASAPPASGGGLD Seq44 363IRMTVIATGFSNEPQPLPQKSRTVPPPPPSFRREASAPRTVNPVEPSPQPKPPTQTGGLD  *********     *   *              * *     * * *   **   **** Seq40 381IPAFLQRK Seq44 423 IPEFLQRR ** ****

Any of the conserved amino acids and conserved domains illustrated bythe sequence comparisons shown above can be expressed in cells (e.g.,via a transgene or expression cassette introduced into a host cell) toincrease the activity of the FtsZ proteins described herein.

Any of the conserved amino acids and conserved domains illustrated bythe sequence comparisons shown above can be deleted in cells) to reducethe expression and/or activity of the (e.g., endogenous) FtsZ proteins.

Ftn2 Sequences

As illustrated herein, cyanobacterial populations that overexpress Ftn2proteins have an increased mean cell size or length. For example, themean cell length of Ftn2 overexpressing cyanobacterial cells is at least150%, or at least 200%, or at least 250%, or at least 300%, or at least500%, or at least 750%, or at least 1000%, or at least 5000%, or atleast 10000%, or at least 15000%, or at least 20000% greater than a wildtype population of cyanobacteria of the same species.

One sequence for a Synechococcus elongatus Ftn2 polypeptide has thefollowing sequence (SEQ ID NO:45).

1 VRIPLDYYRI LCVGVQASAD KLAESYRDRL NQSPSHEFSE 41 LALQARRQLL EAAIAELSDPEQRDRYDRRF FQGGLEAIEP 61 SLELEDWQRI GALLILLELG EYDRVSQLAE ELLPDYDASA 121EVRDQFARGD IALAIALSQQ SLGRECRQQG LYEQAAQHFG 161 RSQSALADHQ RFPELSRTLHQEQGQLRPYR ILERLAQPLT 201 ADSDRQQGLL LLQAMLDDRQ GIEGPGDDGS GLTLDNFLMF241 LQQIRGYLTL AEQQLLFESE ARRPSPAASF FACYTLIARG 281 FCDHQPSLIHRASLLLHELK SRMDVHIEQA IASLLLGQPE 321 EAEALLVQSQ DEETLSQIRA LAQGEALIVGLCRFTETWLA 361 TKVFPDFRDL KERTAPLQPY FDDPDVQTYL DAIVELPSDL 401MPTPLPVEPL EVRSSLLAKE LPTPATPGVA PPPRRRRRDR 441 SERPARTAKR LPLPWIGLGVVVVLGGGTGV WAWRSRSNST 481 PPTPPPVVQT LPEAVPAPSP APVTVALDRA QAETVLQNWL521 AAKAAALGPQ YDRDRLATVL TGEVLQTWQG FSSQQANTQL 561 TSQFDHKLTVDSVQLSDGDQ RAVVQAKVDE VEQVYRGDQL 601 LETRRDLGLV IRYQLVRENN IWKIASISLV RA nucleic acid that encodes the polypeptide with SEQ ID NO:45 has thesequence shown below as SEQ ID NO:46.

1 GTGCGTATTC CTCTCGATTA CTACCGAATT CTCTGTGTTG 41 GCGTGCAAGC CTCGGCAGACAAACTTGCCG AAAGCTACCG 81 CGATCGCCTC AACCAATCGC CCTCCCATGA GTTTTCAGAG 121CTGGCATTGC AGGCGCGGCG GCAACTCCTC GAAGCAGCGA 161 TTGCTGAGCT GAGTGATCCCGAACAGCGCG ATCGCTACGA 201 TCGCCGCTTT TTTCAGGGCG GTCTGGAAGC GATTGAACCA241 AGCCTAGAAC TCGAAGACTG GCAGCGAATT GGAGCCCTGC 281 TGATCCTGCTGGAATTGGGG GAATACGATC GCGTTTCGCA 321 ACTGGCTGAG GAACTCCTGC CAGACTACGACGCGAGCGCA 361 GAAGTACGCG ATCAGTTCGC GCGGGGTGAT ATCGCCTTGG 401CGATCGCACT ATCCCAGCAA TCCCTCGGTC GAGAATGCCG 441 TCAGCAGGGT CTGTACGAACAGGCCGCCCA GCACTTTGGC 481 CGCAGCCAGT CTGCCCTAGC CGATCATCAG CGCTTTCCTG521 AACTGAGTCG AACCCTGCAC CAAGAACAAG GACAGCTACG 561 GCCCTATCGCATTTTGGAGC GGTTGGCCCA GCCCTTGACT 601 GCCGATAGCG ATCGCCAGCA GGGTTTGCTGTTGTTGCAGG 641 CGATGTTGGA CGACCGGCAG GGCATTGAAG GCCCTGGGGA 681TGATGGCTCG GGGCTGACCC TTGATAACTT TTTGATGTTT 721 CTCCAGCAAA TTCGCGGCTATCTGACCCTG GCTGAACAGC 761 AGTTGCTGTT TGAATCGGAA GCGCGTCGGC CCTCGCCGGC801 TGCGAGCTTT TTTGCCTGCT ACACCCTGAT TGCGCGGGGC 841 TTTTGCGATCACCAACCCTC GTTGATCCAT CGCGCCAGCT 881 TGCTCTTGCA TGAACTCAAG AGCCGCATGGATGTGCACAT 921 CGAACAGGCG ATCGCCAGCC TATTGCTCGG ACAGCCCGAA 961GAAGCTGAGG CGCTACTCGT CCAGAGCCAA GATGAGGAAA 1001 CCCTCAGCCA AATCCGTGCCCTAGCCCAAG GGGAAGCCCT 1121 GATCGTCGGT TTGTGCCGAT TCACGGAAAC CTGGCTAGCG1161 ACCAAGGTAT TTCCGGATTT CCGCGACCTC AAGGAAAGGA 1201 CTGCGCCGCTGCAGCCCTAC TTTGACGACC CCGATGTCCA 1241 GACCTATCTG GATGCGATCG TGGAGTTGCCGTCCGATTTG 1281 ATGCCAACGC CGCTACCCGT TGAGCCGCTT GAGGTGCGAT 1321CGTCGTTGCT GGCCAAGGAA CTGCCGACCC CAGCAACGCC 1361 TGGTGTAGCT CCACCCCCTCGCCGCCGTCG CCGCGATCGC 1401 TCCGAACGTC CTGCTCGCAC GGCCAAACGC TTGCCCTTGC1441 CCTGGATTGG TTTGGGGGTT GTGGTGGTTC TCGGCGGTGG 1481 AACAGGGGTTTGGGCTTGGC GATCGCGTTC CAATTCCACC 1521 CCGCCGACCC CGCCCCCCGT GGTTCAAACGCTGCCTGAGG 1561 CGGTACCTGC CCCTTCGCCC GCGCCAGTTA CCGTTGCCCT 1601CGATCGGGCT CAGGCTGAAA CTGTGTTGCA AAACTGGTTG 1641 GCCGCTAAAG CTGCAGCCTTGGGGCCTCAA TACGATCGCG 1681 ATCGCTTAGC GACGGTGCTG ACCGGTGAGG TTCTGCAGAC1721 TTGGCAGGGT TTTTCTAGCC AGCAGGCCAA CACCCAGCTC 1761 ACATCACAGTTCGATCACAA GTTAACCGTC GACTCAGTTC 1801 AGCTCAGTGA CGGTGATCAA CGAGCAGTAGTCCAAGCCAA 1841 GGTCGATGAA GTTGAGCAGG TCTATCGAGG CGACCAGCTG 1881CTCGAAACGC GCCGAGATTT GGGCTTGGTG ATCCGCTACC 1921 AGCTCGTGCG CGAGAACAACATCTGGAAAA TTGCTTCGAT 1961 TAGTTTGGTG CGCTAG

Any of the conserved amino acids and conserved domains illustrated bythe sequence comparisons shown above can be expressed in cells (e.g.,via a transgene or expression cassette introduced into a host cell) toincrease the activity of the Ftn2proteins described herein.

Any of the conserved amino acids and conserved domains illustrated bythe sequence comparisons shown above can be deleted in cells to reducethe activity or expression of the (e.g., endogenous) Ftn2 proteins.

Overexpression of minC, minD, minE, Cdv3, DivIVA, FtsZ, Ftn2 orCombinations Thereof

Populations of cyanobacteria are described herein that include cellsthat with increased activity and/or increased expression of minC, minD,minE, Cdv3, DivIVA, FtsZ, Ftn2, or a combination thereof. In some cases,loss of FtsZ or MinE gene expression or loss of FtsZ or MinE proteinfunction can provide increased cell size. However, in some casesover-expression of FtsZ protein can reduce cell size. Because the Minand Cdv3 proteins can modulate FtsZ function, expression of thoseproteins can be used to modulate cell size.

In some cases, the mean cell length of such cyanobacterial populationscan be at least 150%, or at least 200%, or at least 250%, or at least300%, or at least 500%, or at least 750%, or at least 1000%, or at least3000%, or at least 5000%, or at least 10000%, or at least 15000%, or atleast 20000% greater than a wild type population of cyanobacteria of thesame species.

In some cases, the mean cell length of cyanobacteria in the populationis at least 10%, or at least 15%, or at least 20%, or at least 25%, orat least 30%, or at least 35%, or at least 40%, or at least 45%, or atleast 50% less than a wild type population of cyanobacteria of the samespecies.

Cyanobacteria can be modified to include an expression cassette thatencodes a minC, minD, minE, Cdv3 (DivIVA), FtsZ, or Ftn2 protein, and anoperably linked promoter to drive such expression. In some cases,cyanobacterial cell size is modulated by recombinant expression of acombination of minC, minD, minE, Cdv3 (DivIVA), FtsZ, and/or Ftn2polypeptides using convenient vectors, and expression systems. Theinvention therefore provides expression cassettes or vectors useful forexpressing minC, minD, minE, Cdv3 (DivIVA), FtsZ and/or Ftn2polypeptide(s). In general, overexpression of MinC, MinE, Cdv3, and/orFtn2 increases cell size. Overexpression of MinD leads to a bifurcateddistribution of both large and small cells. Overexpression of FtsZ canreduce cell size.

The expression cassettes or vectors can include a promoter. A promoteris a nucleotide sequence that controls expression of an operably linkednucleic acid sequence by providing a recognition site for RNApolymerase, and possibly other factors, required for propertranscription. A promoter includes a minimal promoter, consisting onlyof all basal elements needed for transcription initiation, such as aTATA-box and/or other sequences that serve to specify the site oftranscription initiation. A promoter may be obtained from a variety ofdifferent sources. For example, a promoter may be derived entirely froma native gene, be composed of different elements derived from differentpromoters found in nature, or be composed of nucleic acid sequences thatare entirely synthetic. A promoter may be derived from many differenttypes of organisms and tailored for use within a given cell.

Any promoter able to direct transcription of an encoded peptide orpolypeptide may be used. Accordingly, many promoters may be includedwithin the expression cassette. Some useful promoters includeconstitutive promoters, inducible promoters, regulated promoters, cellspecific promoters, viral promoters, and synthetic promoters.Particularly useful promoters are inducible promoters, especially thoseinduced by inexpensive signals, or promoters that are auto-inducingunder certain environmental conditions (e.g. a relatively densecyanobacterial population).

For expression of a minC, minD, minE, Cdv3 (DivIVA), FtsZ and/or Ftn2polypeptide in a bacterium or cyanobacterium, an expression cassette canbe used that has a nucleic acid segment encoding the minC, minD, minE,Cdv3 (DivIVA), FtsZ and/or Ftn2 polypeptide and a promoter operablylinked thereto. Such a promoter can be any DNA sequence capable ofbinding a RNA polymerase and initiating the downstream (3″)transcription of a coding sequence into mRNA. A promoter has atranscription initiation region that is usually placed proximal to the5′ end of the coding sequence. This transcription initiation regionusually includes an RNA polymerase binding site and a transcriptioninitiation site. A second domain called an operator may be present andoverlap an adjacent RNA polymerase binding site at which RNA synthesisbegins. The operator permits negatively regulated (inducible)transcription, as a gene repressor protein may bind the operator andthereby inhibit transcription of a specific gene.

Constitutive expression may occur in the absence of negative regulatoryelements, such as the operator. In addition, positive regulation may beachieved by a gene activator protein binding sequence, which, if presentis usually proximal (5′) to the RNA polymerase binding sequence. Anexample of a gene activator protein is the catabolite activator protein(CAP), which helps initiate transcription of the lac operon in E. coli(Raibaud et al., Ann. Rev. Genet., 18:173 (1984)). Regulated expressionmay therefore be positive or negative, thereby either enhancing orreducing transcription.

Other examples of promoters that can be employed include promoters ofsugar metabolizing enzymes, such as galactose, lactose (lac) (Chang etal., Nature, 198:1056 (1977), and maltose. Additional examples includepromoter sequences derived from biosynthetic enzymes such as tryptophan(Trp) (Goeddel et al., Nuc. Acids Res., 8:4057 (1980); Yelverton et al.,Nuc. Acids Res., 9:731 (1981); U.S. Pat. No. 4,738,921; and EPO Publ.Nos. 036 776 and 121 775). The β-lactamase (bla) promoter system(Weissmann, “The cloning of interferon and other mistakes”, in:Interferon 3 (ed. I. Gresser), 1981), and bacteriophage lambda P_(L)(Shimatake et al., Nature, 292:128 (1981)) and T5 (U.S. Pat. No.4,689,406) promoter systems also provide useful promoter sequences. Apreferred promoter is the Chlorella virus promoter (U.S. Pat. No.6,316,224).

Synthetic promoters that do not occur in nature also function aspromoters in cyanobacterial cells. For example, transcription activationsequences of one bacterial or bacteriophage promoter may be joined withthe operon sequences of another bacterial or bacteriophage promoter,creating a synthetic hybrid promoter (U.S. Pat. No. 4,551,433). Forexample, the tac promoter is a hybrid trp-lac promoter comprised of bothtrp promoter and lac operon sequences that is regulated by the lacrepressor (Amann et al., Gene, 25:167 (1983); de Boer et al., Proc.Natl. Acad. Sci. USA, 80:21 (1983)). Furthermore, a bacterial orcyanobacterial promoter can include naturally occurring promoters ofnon-bacterial origin that have the ability to bind RNA polymerase andinitiate transcription in cyanobacteria. A naturally occurring promoterof non-bacterial origin can also be coupled with a compatible RNApolymerase to produce high levels of expression of some genes inprokaryotes. The bacteriophage T7 RNA polymerase/promoter system is anexample of a coupled promoter system (Studier et al., J. Mol. Biol.,189:113 (1986); Tabor et al., Proc. Natl. Acad. Sci. USA, 82:1074(1985)). In addition, a hybrid promoter can also be comprised of abacteriophage promoter and an E. coli operator region (EPO Publ. No. 267851).

In some cases, quorum sensing-responsive promoters can be employed inthe expression cassettes/vectors. Quorum sensing is a mechanism wherebybacteria are able to indirectly detect the concentration of neighboringcells. A quorum sensing pathway is one that is usually activated when abacterial population becomes concentrated. For example, biofilmformation is controlled often by quorum sensing. Such quorum sensingpromoters can make cyanobacteria self-induce the genes of interest whena certain cell concentration is reached (e.g., when the cells are ready,or will soon be ready, to be harvested), without the addition ofchemical inducers. See, e.g., Miller, Melissa B., and Bonnie L. Bassler.“Quorum sensing in bacteria.” Annual Reviews in Microbiology 55(1):165-199 (2001).

In some cases, the promoter can become active at certain times duringculture or fermentation. For example, the promoter can in some cases beactive before, during, or after log phase growth of the cells duringculture or fermentation.

For example, LuxI/LuxR genes are a family of genes that produce quorumsensing behavior in bacteria. See, e.g., Waters & Bassler, “Quorumsensing: cell-to-cell communication in bacteria,” Annu Rev Cell Dev Biol21: 319-46 (2005). Quorum sensing pathways in natural contexts involve amicrobe that is capable of producing a diffusible molecule that can passthrough the cell membrane, such as the class of molecules calledacyl-homoserine lactones (AHL). These molecules can diffuse from thecell that produces them to the outside environment, and then back intoother neighboring bacteria. When the concentration of AHL of a specifictype becomes high enough, it can stabilize a transcription factor thatturns on specific genes. Usually, quorum sensing pathways are utilizedfor a bacteria to sense how large its population is—the more surroundingbacteria in the environment, the higher the AHL levels. At a certaincell density, the AHL builds up to a level that it can bind a receptorprotein (e.g. LuxR), stabilizing it and allowing for downstream generegulation.

Quorum sensing-responsive promoters can be used in any of the expressioncassettes or expression vectors described herein. For example,cyanobacteria expressing LuxI (or similar protein) can make an AHLsignal that could then build up as the density of the cyanobacteriaincreases. When the cells become dense enough, they can turn on theexpression of genes like Cdv3, arresting division and causingauto-induction of the elongation process.

One example of a protein that can modulate quorum sensing-responsivepromoters is the LuxI from Vibrio fishcheri, with the following sequence(SEQ ID NO:47).

1 MIKKSDFLGI PSEEYRGILS LRYQVFKRRL EWDLVSEDNL 41 ESDEYDNSNA EYIYACDDAEEVNGCWRLLP TTGDYMLKTV 81 FPELLGDQVA PRDPNIVELS RFAVGKNSSK INNSASEITM 121KLFQAIYKHA VSQGITEYVT VTSIAIERFL KRIKVPCHRI 161 GDKEIHLLGN TRSVVLSMPINDQFRKAVSNA nucleic acid encoding this Vibrio fishcheri LuxI protein shown below(SEQ ID NO:48).

1 ATGATAAAAA AATCGGACTT TTTGGGCATT CCATCAGAGG 41 AGTATAGAGG TATTCTTAGTCTTCGTTATC AGGTATTTAA 81 ACGAAGACTG GAGTGGGACT TGGTAAGTGA GGATAATCTT 121GAATCAGATG AATATGATAA CTCAAATGCA GAATATATTT 161 ATGCTTGTGA TGATGCGGAAGAGGTAAATG GCTGTTGGCG 201 TTTGTTACCT ACAACGGGTG ATTACATGTT AAAAACTGTT241 TTTCCTGAAT TGCTCGGAGA TCAAGTAGCC CCAAGAGATC 281 CAAATATAGTCGAATTAAGC CGTTTTGCTG TGGGAAAAAA 321 TAGCTCAAAA ATAAATAACT CTGCTAGTGAAATAACAATG 361 AAATTGTTTC AAGCTATATA TAAACACGCA GTTAGTCAAG 401GTATTACAGA ATATGTAACA GTAACATCAA TAGCAATAGA 441 GCGATTTCTG AAACGTATTAAAGTTCCTTG TCATCGCATT 481 GGTGATAAGG AGATTCATTT ATTAGGTAAT ACTAGATCTG521 TTGTATTGTC TATGCCTATT AATGATCAGT TTAGAAAAGC 561 TGTATCAAAT TAA

A sequence of a LuxR receptor protein from Vibrio fishcheri is shownbelow (SEQ ID NO:49).

1 MIYNTQNLRQ TIGKDKEMGM KNINADDTYR IINKIKACRS 41 NNDINQCLSD MTKMVHCEYYLLAIIYPHSM VKSDISILDN 81 YPKKWRQYYD DANLIKYDPI VDYSNSNHSP INWNIFENNA 121VNKKSPNVIK EAKTSGLITG FSFPIHTANN GFGMLSFAHS 161 EKDNYIDSLF LHACMNIPLIVPSLVDNYRK INIANNKSNN 201 DLTKREKECL AWACEGKSSW DISKILGCSE RTVTFHLTNA241 QMKLNTTNRC QSISKAILTG AIDCPYFKNA nucleic acid sequence for this LuxR protein from Vibrio fishcheri isprovided below as SEQ ID NO:50.

1 ATGATATATA ACACGCAAAA CTTGCGACAA ACAATAGGTA 41 AGGATAAAGA GATGGGTATGAAAAACATAA ATGCCGACGA 81 CACATACAGA ATAATTAATA AAATTAAAGC TTGTAGAAGC 121AATAATGATA TTAATCAATG CTTATCTGAT ATGACTAAAA 161 TGGTACATTG TGAATATTATTTACTCGCGA TCATTTATCC 201 TCATTCTATG GTTAAATCTG ATATTTCAAT TCTAGATAAT241 TACCCTAAAA AATGGAGGCA ATATTATGAT GACGCTAATT 281 TAATAAAATATGATCCTATA GTAGATTATT CTAACTCCAA 321 TCATTCACCA ATTAATTGGA ATATATTTGAAAACAATGCT 361 GTAAATAAAA AATCTCCAAA TGTAATTAAA GAAGCGAAAA 401CATCAGGTCT TATCACTGGG TTTAGTTTCC CTATTCATAC 441 GGCTAACAAT GGCTTCGGAATGCTTAGTTT TGCACATTCA 481 GAAAAAGACA ACTATATAGA TAGTTTATTT TTACATGCGT521 GTATGAACAT ACCATTAATT GTTCCTTCTC TAGTTGATAA 561 TTATCGAAAAATAAATATAG CAAATAATAA ATCAAACAAC 601 GATTTAACCA AAAGAGAAAA AGAATGTTTAGCGTGGGCAT 641 GCGAAGGAAA AAGCTCTTGG GATATTTCAA AAATATTAGG 681CTGCAGTGAG CGTACTGTCA CTTTCCATTT AACCAATGCG 721 CAAATGAAAC TCAATACAACAAACCGCTGC CAAAGTATTT 761 CTAAAGCAAT TTTAACAGGA GCAATTGATT GCCCATACTT801 TAAAAATTAA

An example of a LuxR-responsive promoter from Vibrio fishcheri is shownbelow as (SEQ ID NO:51).

1 TGTCGCAAGT TTTGCGTGTT ATATATCATT AAAACGGTAA 41TGGATTGACA TTTGATTCTA ATAAATTGGA TTTTTGTCAC 81ACTATTGTAT CGCTGGGAAT ACAATTACTT AACATAAGCA 121CCTGTAGGAT CGTACAGGTT TACGCAAGAA AATGGTTTGT 161TATAGTCGAA TGAATTCATT AAAGAGGAGA AAGGTACCWhen LuxR is expressed and stabilized (because AHL is present), the LuxRprotein binds to a promoter sequence like that shown above as (SEQ IDNO:51) and drives gene expression from it.

It is understood that many promoters and associated regulatory elementsmay be used within the expression cassette/vector to transcribe an RNAencoding a minC, minD, minE, Cdv3 (DivIVA), FtsZ and/or Ftn2polypeptide. The promoters described above are provided merely asexamples and are not to be considered as a complete list of promotersthat are included within the scope of the invention.

The expression cassette of the invention may contain a nucleic acidsequence for increasing the translation efficiency of an mRNA encoding aminC, minD, minE, Cdv3 (DivIVA), FtsZ and/or Ftn2 polypeptide. Suchincreased translation serves to increase production of the polypeptide.The presence of an efficient ribosome binding site is useful for geneexpression in prokaryotes. In bacterial mRNA, a conserved stretch of sixnucleotides, the Shine-Dalgarno sequence, is usually found upstream ofthe initiating AUG codon. (Shine et al., Nature, 254:34 (1975)). Thissequence is thought to promote ribosome binding to the mRNA by basepairing between the ribosome binding site and the 3′ end of Escherichiacoli 16S rRNA. (Steitz et al., “Genetic signals and nucleotide sequencesin messenger RNA”, in: Biological Regulation and Development: GeneExpression (ed. R. F. Goldberger), 1979)). Such a ribosome binding site,or operable derivatives thereof, are included within the expressioncassette of the invention.

A translation initiation sequence can be derived from any expressedbacterial or cyanobacterial gene and can be used within an expressioncassette/vector of the invention. Preferably the gene from which thetranslation initiation sequence is obtained is a highly expressed gene.A translation initiation sequence can be obtained via standardrecombinant methods, synthetic techniques, purification techniques, orcombinations thereof, which are all well known. (Ausubel et al., CurrentProtocols in Molecular Biology, Green Publishing Associates and WileyInterscience, N Y. (1989); Beaucage and Caruthers, Tetra. Letts.,22:1859 (1981); VanDevanter et al., Nucleic Acids Res., 12:6159 (1984).Alternatively, translational start sequences can be obtained fromnumerous commercial vendors. (Operon Technologies; Life TechnologiesInc, Gaithersburg, Md.). In some embodiments, the T7 translationinitiation sequence is used. The T7 translation initiation sequence isderived from the highly expressed T7 Gene 10 cistron and can have asequence that includes TCTAGAAATAATTTTGTTTAACTTTAAGAA GGAGATATA (SEQ IDNO:52). Other examples of translation initiation sequences include, butare not limited to, the maltose-binding protein (Mal E gene) startsequence (Guan et al., Gene, 67:21 (1997)) present in the pMalc2expression vector (New England Biolabs, Beverly, Mass.) and thetranslation initiation sequence for the following genes: thioredoxingene (Novagen, Madison, Wis.), Glutathione-S-transferase gene(Pharmacia, Piscataway, N.J.), β-galactosidase gene, chloramphenicolacetyltransferase gene and E. coli Trp E gene (Ausubel et al., 1989,Current Protocols in Molecular Biology, Chapter 16, Green PublishingAssociates and Wiley Interscience, NY).

The invention therefore provides an expression cassette or vector thatincludes a promoter operable in a selected host and a nucleic acidencoding one or more of the minC, minD, minE, Cdv3, (DivIVA), FtsZand/or Ftn2 polypeptides described herein. The expression cassette canhave other elements, for example, termination signals, origins ofreplication, enhancers, and the like as described herein. The expressioncassette can also be placed in a vector for easy replication andmaintenance.

An expression cassette or nucleic acid construct of the invention isthought to be particularly advantageous for inducing expression of thepolypeptides.

Loss-of-Function

Populations of cyanobacteria are also described herein that includecyanobacterial cells that with reduced activity and/or expression ofminC, minD, or a combination thereof where the mean cell length ofcyanobacteria in the population is at least 10%, or at least 15%, or atleast 20%, or at least 25%, or at least 30%, or at least 35%, or atleast 40%, or at least 45%, or at least 50% less than a wild typepopulation of cyanobacteria of the same species. The cyanobacterialpopulations are modified either to reduce the expression of at least oneof minC and minD, or to reduce the function or activity of at least oneof minC and minD. In other words, the minC and/or minD genes in thecyanobacterial populations can have mutations in the transcriptionalregulatory elements, or in the coding region of these genes. In somecases the populations of cyanobacteria have one or more genomicdeletions, insertions, or substitutions in at least a portion of thecoding region of the minC gene, the minD gene, or a combination thereof.Such mutations can be generated by site-specific recombination-mediatedmethods for deleting unwanted genetic elements from plant and animalcells. The deletions can range in size from a few base pairs tothousands of nucleotides (or any value therebetween). Deletions can becreated at a desired location in the genome, for example, by selectingborders (end points) of the deletions at defined locations to controlthe size of the deletion.

In some cases, a native minC gene, a native minD gene, or a combinationthereof is deleted, or mutated to reduce the function of the minC orminD protein, and one or more expression cassettes is introduced thatincludes a coding region for minC, minD, minE, Cdv3 (DivIVA), FtsZand/or Ftn2, where each coding region is under the control of aninducible or regulatable promoter.

Non-limiting examples of methods of introducing a modification into thegenome of a cell can include use of microinjection, viral delivery,recombinase technologies, homologous recombination, TALENS, CRISPR,and/or ZFN, see, e.g. Clark and Whitelaw Nature Reviews Genetics4:825-833 (2003); which is incorporated by reference herein in itsentirety.

For example, nucleases such as zinc finger nucleases (ZFNs),transcription activator like effector nucleases (TALENs), and/ormeganucleases can be employed with a guide nucleic acid that allows thenuclease to target the genomic MinC and/or MinD site(s). In some cases,a targeting vector can be used to introduce a deletion or modificationof one or more genomic MinC and/or MinD site(s).

A “targeting vector” is a vector generally has a 5′ flanking region anda 3′ flanking region homologous to segments of the gene of interest. The5′ flanking region and a 3′ flanking region can surround a DNA sequencecomprising a modification and/or a foreign DNA sequence to be insertedinto the gene. For example, the foreign DNA sequence may encode aselectable marker. In some cases, the targeting vector does not comprisea selectable marker but such a selectable marker can facilitateidentification and selection of cells with desirable mutations. Examplesof suitable selectable markers include antibiotics resistance genes suchas chloramphenicol resistance, gentamycin resistance, kanamycinresistance, spectinomycin resistance (SpecR), neomycin resistance gene(NEO), and/or the hygromycin β-phosphotransferase genes. The 5′ flankingregion and the 3′ flanking region can be homologous to regions withinthe gene, or to regions flanking the gene to be deleted, modified, orreplaced with the unrelated DNA sequence.

The targeting vector is contacted with the native gene of interest invivo (e.g., within the cell) under conditions that favor homologousrecombination. For example, the cell can be contacted with the targetingvector under conditions that result in transformation of thecyanobacterial cell(s) with the targeting vector.

A typical targeting vector contains nucleic acid fragments of not lessthan about 0.1 kb nor more than about 10.0 kb from both the 5′ and the3′ ends of the genomic locus which encodes the gene to be modified (e.g.the genomic MinC and/or MinD site(s)). These two fragments are separatedby an intervening fragment of nucleic acid which encodes themodification to be introduced. When the resulting construct recombineshomologously with the chromosome at this locus, it results in theintroduction of the modification, e.g. a deletion of a portion of thegenomic MinC and/or MinD site(s), replacement of the genomic MinC and/orMinD promoter or coding region site(s), or the insertion ofnon-conserved codon or a stop codon.

In some cases, a Cas9/CRISPR system can be used to create a modificationin genomic MinC and/or MinD site(s). Clustered regularly interspacedshort palindromic repeats (CRISPR)/CRISPR-associated (Cas) systems areuseful for, e.g. RNA-programmable genome editing (see e.g., Marraffiniand Sontheimer. Nature Reviews Genetics 11: 181-190 (2010); Sorek et al.Nature Reviews Microbiology 2008 6: 181-6; Karginov and Hannon. Mol Cell2010 1:7-19; Hale et al. Mol Cell 2010:45:292-302; Jinek et al. Science2012 337:815-820; Bikard and Marraffini Curr Opin Immunol 2012 24:15-20;Bikard et al. Cell Host & Microbe 2012 12: 177-186; all of which areincorporated by reference herein in their entireties). A CRISPR guideRNA can be used that can target a Cas enzyme to the desired location inthe genome, where it generates a double strand break. This technique isdescribed, for example, by Mali et al. Science 2013 339:823-6; which isincorporated by reference herein in its entirety. Kits for the designand use of CRISPR-mediated genome editing are commercially available,e.g. the PRECISION X CAS9 SMART NUCLEASE™ System (Cat No. CAS900A-1)from System Biosciences, Mountain View, Calif.

In other cases, a cre-lox recombination system of bacteriophage P1,described by Abremski et al. 1983. Cell 32:1301 (1983), Sternberg etal., Cold Spring Harbor Symposia on Quantitative Biology, Vol. XLV 297(1981) and others, can be used to promote recombination and alterationof the genomic MinC and/or MinD site(s). The cre-lox system utilizes thecre recombinase isolated from bacteriophage P1 in conjunction with theDNA sequences that the recombinase recognizes (termed lox sites). Thisrecombination system has been effective for achieving recombination inplant cells (see, e.g., U.S. Pat. No. 5,658,772), animal cells (U.S.Pat. Nos. 4,959,317 and 5,801,030), and in viral vectors (Hardy et al.,J. Virology 71:1842 (1997).

The populations of cyanobacteria described herein have genomic mutationsthat modulate or replace the promoter regions of minC, minD, minE, Cdv3,and/or DivIVA genes.

The populations of cyanobacteria described herein have genomic mutationsthat alter one or more amino acids in the encoded MinC protein, theencoded MinD protein, or in both the MinC protein and the MinD protein.For example, cyanobacteria can be modified so that in the encoded MinCprotein, the encoded MinD protein, or in both the MinC protein and theMinD protein is more prone to degradation, or is less stable, so thatthe half-life of such protein(s) is reduced. In another example,cyanobacteria can be modified so that at least one amino acid of a minCor mind polypeptide is deleted or mutated to reduce the enzymaticactivity at least one of minC and minD. In some cases, a conserved aminoacid or a conserved domain of the minC or mind polypeptide is modified.For example, a conserved amino acid or several amino acids in aconserved domain of the minC or mind polypeptide can be replaced withone or more amino acids having physical and/or chemical properties thatare different from the conserved amino acid(s). For example, to changethe physical and/or chemical properties of the conserved amino acid(s),the conserved amino acid(s) can be deleted or replaced by amino acid(s)of another class, where the classes are identified in the followingTable 1.

TABLE 1 Classification Genetically Encoded Hydrophobic Aromatic F, Y, WApolar M, G, P Aliphatic A, V, L, I Hydrophilic Acidic D, E Basic H, K,R Polar Q, N, S, T, Y Cysteine-Like C

Different types of amino acids can be employed in the minC and/or mindpolypeptide.

TABLE 2 Amino Acid One-Letter Symbol Common Abbreviation Alanine A AlaArginine R Arg Asparagine N Asn Aspartic acid D Asp Cysteine C CysGlutamine Q Gln Glutamic acid E Glu Glycine G Gly Histidine H HisIsoleucine I Ile Leucine L Leu Lysine K Lys Methionine M MetPhenylalanine F Phe Proline P Pro Serine S Ser Threonine T ThrTryptophan W Trp Tyrosine Y Tyr Valine V Val β-Alanine bAlaN-Methylglycine MeGly (sarcosine) Ornithine Orn Norleucine NlePenicillamine Pen Homoarginine hArg N-methylvaline MeVal HomocysteinehCys Homoserine hSerTypes of Cyanobacteria

Any cyanobacteria can be modified to reduce cell length or to increasethe cell length, either permanently or transiently. The cell sizes ofany cyanobacterial species can be modulated using the methods describedherein.

In some cases, the cell sizes of rod-shaped or filamentous cyanobacteriaare modulated. Examples of cyanobacterial species that can be changedinclude Synechococcus elongatus sp. PCC 7942; Synechococcus elongatus7002; Synechococcus elongatus UTEX 2973; Anthropira platensis; andLeptolyngbya sp. strain BL0902. Synechococcus elongatus sp. PCC 7942 isone of the dominant model organisms, providing a variety of usefulgenetic tools. Synechococcus elongatus 7002 is a well-developed modelorganism with improved productivity and resilience. Synechococcuselongatus UTEX 2973 is related to S. elongatus 7942, and it has greatlyimproved growth properties. Anthropira platensis is perhaps the mostbroadly utilized cyanobacteria in scaled applications. Leptolyngbya sp.strain BL0902 is a bioindustrial strain whose genetic make-up is not aswell-studied as some of the model cyanobacterial species.

Further examples of cyanobacterial species that can be modified include,for example, any of those in Table 3.

TABLE 3 Types of Cyanobacteria Species Lineage Release SynechococcusCyanobacteria; Oscillatorio- American Type Culture elongatus sp. PCC7942 phycideae; Chroococcales; Collection, ATCC Synechococcus accessionno. 33912. Synechococcus Cyanobacteria; Oscillatorio- UTEX CultureCollection elongatus UTEX 2973 phycideae; Chroococcales; of Algae,University of Synechococcus Texas at Austin Anthropira platensisCyanobacteria; Oscillatorio- American Type Culture phycideae;Oscillatoriales; Collection, ATCC Arthrospira accession no. 29408.Prochlorococcus Cyanobacteria; Prochlorales; The Gordon and Bettymarinus str. AS9601 Prochlorococcaceae; Moore Foundation MarineProchlorococcus Microbiology Initiative (2007) Acaryochloris marinaCyanobacteria; Acaryochloris TGen Sequencing Center MBIC11017 (2008)Anabaena sp. PCC 7120 Cyanobacteria; Nostocales; Kazusa (2001)Nostocaceae; Nostoc Anabaena variabilis Cyanobacteria; Nostocales; JGI(2007) ATCC 29413 Nostocaceae; Anabaena Synechococcus sp. Cyanobacteria;Chroococcales; TIGR (2006) CC9311 Synechococcus Cyanothece sp. ATCCCyanobacteria; Chroococcales; Washington University 51142 Cyanothece(2008) Chlorobium tepidum Chlorobi; Chlorobia; TIGR (2002) TLSChlorobiales; Chlorobiaceae; Chlorobaculum Synechococcus sp. JA-3-Cyanobacteria; Chroococcales; TIGR (2007) 3Ab Synechococcus Cyanothecesp. PCC Cyanobacteria; Chroococcales; 7425 Cyanothece Synechococcus sp.JA-2- Cyanobacteria; Chroococcales; TIGR (2007) 3B′a(2-13) SynechococcusGloeobacter violaceus Cyanobacteria; Gloeobacteria; Kazusa (2003) PCC7421 Gloeobacterales; Gloeobacter Prochlorococcus Cyanobacteria;Prochlorales; JGI (2003) marinus MED4 Prochlorococcaceae;Prochlorococcus Microcystis aeruginosa Cyanobacteria; Chroococcales;Kazusa, U. Tsukuba, NIES NIES-843 Microcystis (2007) ProchlorococcusCyanobacteria; Prochlorales; JGI (2003) marinus MIT9313Prochlorococcaceae; Prochlorococcus Prochlorococcus Cyanobacteria;Prochlorales; The Gordon and Betty marinus str. NATL1AProchlorococcaceae; Moore Foundation Marine Prochlorococcus MicrobiologyInitiative (2007) Arthrospira platensis Cyanobacteria; Oscillatoriales;NIES-39 Arthrospira; Arthrospira platensis Nostoc punctiformeCyanobacteria; Nostocales; JGI (2008) ATCC 29133 Nostocaceae; NostocProchlorococcus Cyanobacteria; Prochlorales; The Gordon and Bettymarinus str. MIT 9211 Prochlorococcaceae; Moore Foundation MarineProchlorococcus Microbiology Initiative (2008) ProchlorococcusCyanobacteria; Prochlorales; JGI (2007) marinus str. MIT 9215Prochlorococcaceae; Prochlorococcus Prochlorococcus Cyanobacteria;Prochlorales; The Gordon and Betty marinus str. MIT 9301Prochlorococcaceae; Moore Foundation Marine Prochlorococcus MicrobiologyInitiative (2007) Prochlorococcus Cyanobacteria; Prochlorales; TheGordon and Betty marinus str. MIT 9303 Prochlorococcaceae; MooreFoundation Marine Prochlorococcus Microbiology Initiative (2007)Prochlorococcus Cyanobacteria; Prochlorales; The Gordon and Bettymarinus str. MIT 9515 Prochlorococcaceae; Moore Foundation MarineProchlorococcus Microbiology Initiative (2007) SynechococcusCyanobacteria; Chroococcales; Nagoya U. (2007) elongatus PCC 6301Synechococcus Cyanothece sp. PCC Cyanobacteria; Chroococcales; 7424Cyanothece Cyanothece sp. PCC Cyanobacteria; Chroococcales; 8801Cyanothece Prochlorococcus Cyanobacteria; Prochlorales; JGI (2007)marinus str. NATL2A Prochlorococcaceae; Prochlorococcus ProchlorococcusCyanobacteria; Prochlorales; JGI (2007) marinus str. MIT 9312Prochlorococcaceae; Prochlorococcus Rhodopseudomonas Proteobacteria; JGI(2003) palustris CGA009 Alphaproteobacteria; Rhizobiales;Bradyrhizobiaceae; Rhodopseudomonas Prochlorococcus Cyanobacteria;Prochlorales; Genoscope (2003) marinus SS120 Prochlorococcaceae;Prochlorococcus Synechococcus sp. Cyanobacteria; Chroococcales; JGI(2007) CC9605 Synechococcus Synechococcus sp. Cyanobacteria;Chroococcales; JGI (2007) CC9902 Synechococcus Synechocystis sp. PCCCyanobacteria; Chroococcales; Kazusa (1996, 2002, 2003) 6803Synechocystis Synechococcus sp. PCC Cyanobacteria; Chroococcales; PennState University 7002 Synechococcus (2008) Synechococcus Cyanobacteria;Chroococcales; JGI (2007) elongatus PCC 7942 Synechococcus Synechococcussp. Cyanobacteria; Chroococcales; Genoscope (2007) RCC307 SynechococcusSynechococcus sp. WH Cyanobacteria; Chroococcales; Genoscope (2007) 7803Synechococcus Trichodesmium Cyanobacteria; Oscillatoriales; erythraeumIMS101 Trichodesmium; Trichodesmium erythraeum ThermosynechococcusCyanobacteria; Chroococcales; Kazusa (2002) elongatus BP-1Thermosynechococcus Synechococcus sp. Cyanobacteria; Chroococcales; JGI(2003) WH8102 SynechococcusUseful Products

Cyanobacteria can be used produce a variety of useful products. Examplesinclude oils (fatty acids), alkenes, polyhydroxybutyrate, biomass,carbohydrates, phycocyanin, ethanol, hydrogen, isobutanol, ethylene, andcombinations thereof. Products such as oils (fatty acids), alkenes,ethanol, hydrogen, isobutanol, ethylene, and combinations thereof can beused in manufacturing and as biofuels. For example, ethanol,carbohydrate feedstocks, and biomass can be used to make bioethanol.Polyhydroxybutyrate is useful, for example, in bioplastics. Biomass,carbohydrates, and ethanol can also be used in foods and foodmanufacturing. Ethanol, hydrogen, isobutanol, and ethylene are useful inmanufacturing, as a source of energy, and/or for making fuel.

The following non-limiting Examples describe some of the experimentsperformed.

Example 1: Materials and Methods

This Example describes some of the materials and methods employed in thedevelopment of the invention.

Homolog Search

Identification of putative Min homologs in Synechococcus elongatus PCC7942 was carried out via Basic Local Alignment Search Tool (BlastP) withavailable Min system factors from both Escherichia coli str. K-12substrain MG1655 and Bacillus subtilis subsp. subtilis str. 168. To gaininsight into primary sequence conservation, S. elongatus MinC, MinD,MinE and DivIVA protein sequences were aligned to their homologs in E.coli and B. subtilis using MAFFT alignment v7.017 in Geneious v9.0.4(Blossum62, open gap penalty=1.53, offset value=0.123) (FIGS. 1C-1E,4A-4B). Secondary structure prediction for MinC/D/E was carried outusing Phyre2 (see website at www.sbg.bio.ic.ac.uk/phyre2/), whichperforms automatic homology modeling using MinC/D/E crystal structuresfrom E. coli. The resulting .pdb file was imported into PyMOL v1.76 togenerate figures. Because no complete crystal structure exists forDivIVA, secondary structure prediction was carried out using JPred4 (seewebsite at www.compbio.dundee.ac.uk/jpred/) through the automatedProtein Secondary Structure Prediction Server (Jnet). Identification ofthe DivIVA domain was performed using general Delta-Blast (DomainEnhanced Lookup Time Accelerated Blast; see website atblast.ncbi.nlm.nih.gov/Blast.cgi). Secondary structure prediction forCdv3 was carried out using JPred4 (see website atcompbio.dundee.ac.uk/jpred/) through the automated Protein SecondaryStructure Prediction Server (Jnet).

Construct Designs

Deletion constructs in this study were generated using Gibson Assembly(Gibson et al., Nat Meth 6, 343-345 (2009)) from PCR fragments orsynthesized dsDNA. A list of primers employed is shown in Table 4 below.

TABLE 4 Primer Sequences Knockouts Sequence ΔminC HomologyGGATCTCAAGAAGATCCTTTGATCTAGTCTAGGGATCAGCATTGGG Region 1 ForwardSEQ ID NO: 53 ΔminC HomologyTTATGTCCACTGGGTTCGTGCCTTCCGGAACCACGGGGTAGAGAGC Region 1 ReverseSEQ ID NO: 54 ΔminC HomologyGATCACCAAGGTAGTCGGCAAATAAGGGCACATCTTGAGACGATCG Region 2 ForwardSEQ ID NO: 55 ΔminC HomologyCCTATGGAAAAACGCCAGCAACGCGGAGTCCTCACGCCCGACGTAGTC Region 2 ReverseSEQ ID NO: 56 ΔminD HomologyGGATCTCAAGAAGATCCTTTGATCTGGCGGGCTTGGGCTTCTGTCAG Region 1 ForwardSEQ ID NO: 57 ΔminD HomologyAGCGCTCGAATAAGTCAGCCAGCATAGGGTCCGAAGAGCAGGAGCGG Region 1 ReverseSEQ ID NO: 58 ΔminD HomologyGATCACCAAGGTAGTCGGCAAATAATAATTACTGCCTTGCCGGTGTAG Region 2 ForwardSEQ ID NO: 59 ΔminD HomologyCCTATGGAAAAACGCCAGCAACGCGGCGGATCTCTGGCTGATTTGTC Region 2 ReverseSEQ ID NO: 60 ΔminE HomologyGGATCTCAAGAAGATCCTTTGATCTGGCGGGCTTGGGCTTCTGTCAG Region 1 ForwardSEQ ID NO: 61 ΔminE HomologyAGGTGACAACAATAACGCGACTCATAGGGTCCGAAGAGCAGGAGCGG Region 1 ReverseSEQ ID NO: 62 ΔminE HomologyGATCACCAAGGTAGTCGGCAAATAATAATTACTGCCTTGCCGGTGTAG Region 2 ForwardSEQ ID NO: 63 ΔminE HomologyCCTATGGAAAAACGCCAGCAACGCGGCGGATCTCTGGCTGATTTGTC Region 2 ReverseSEQ ID NO: 64 Δcdv3 HomologyGGATCTCAAGAAGATCCTTTGATCTACTTCACCGACGAAAACCGTG Region 1 ForwardSEQ ID NO: 65 Δcdv3 HomologyTTATGTCCACTGGGTTCGTGCCTTCTCACGTCAGGCGATCGCGCTC Region 1 ReverseSEQ ID NO: 66 Δcdv3 HomologyGATCACCAAGGTAGTCGGCAAATAATTGACGACTACTCGGCTGCATC Region 2 ForwardSEQ ID NO: 67 Δcdv3 HomologyCCTATGGAAAAACGCCAGCAACGCGCTTCAAGATGATCTGAGCTGAG Region 2 ReverseSEQ ID NO: 68 Spectinomycin GAAGGCACGAACCCAGTGGAC SEQ ID NO: 69Cassette Forward Spectinomycin TTATTTGCCGACTACCTTGGTG SEQ ID NO: 70Cassette Reverse Origin of CGCGTTGCTGGCGTTTTTCC SEQ ID NO: 71Replication Forward Origin of AGATCAAAGGATCTTCTTGAG SEQ ID NO: 72Replication Reverse Riboswitch MinC and MinD Reporters SequencemNeonGreen AGCACCCTGCTAAGGAGGCAACAAGATGGTCAGCAAAGGTGAAGAAG ForwardSEQ ID NO: 73 mNeonGreen CTTGTACAGTTCGTCCATACCC SEQ ID NO: 74 ReverseMinC Forward GATGGGTATGGACGAACTGTACAAGATGAGTGACGTAGACGCTTC SEQ ID NO: 75MinC Reverse GCATGCCTGCAGGTCGACTCTAGAACTACTTCCCGCCAGGATCGG SEQ ID NO: 76MinD Forward GATGGGTATGGACGAACTGTACAAGATGAGTCGCGTTATTGTTGTCSEQ ID NO: 77 MinD ReverseGCATGCCTGCAGGTCGACTCTAGAACTAGAGAATTTTTTTATTGAGG SEQ ID NO: 78Native Fluorescent Reporters Sequence minC HomologyGGATCTCAAGAAGATCCTTTGATCTAGTCTAGGGATCAGCATTGGG Region 1 ForwardSEQ ID NO: 79 minC HomologyTGTCTTCTTCACCTTTGCTGACCATCGGAACCACGGGGTAGAGAGC Region 1 ReverseSEQ ID NO: 80 minC HomologyTTTGATGCTCGATGAGTTTTTCTAAGGGCACATCTTGAGACGATCG Region 2 ForwardSEQ ID NO: 81 minC HomologyCCTATGGAAAAACGCCAGCAACGCGGAGTCCTCACGCCCGACGTAG Region 2 ReverseSEQ ID NO: 82 cdv3 HomologyGGATCTCAAGAAGATCCTTTGATCTGACGGTCAACTATGCGCGCCAAC Region 1 ForwardSEQ ID NO: 83 cdv3 HomologyTGTCTTCTTCACCTTTGCTGACCATGCGCGATCGCCGACGGGGAGC Region 1 ReverseSEQ ID NO: 84 mNeonGreen ATGGTCAGCAAAGGTGAAGAAG SEQ ID NO: 85 ForwardmNeonGreen TTTTGAGACACAACGTGGCTTTCCCTCACTTGTACAGTTCGTCC ReverseSEQ ID NO: 86 cdv3 HomologyTTTGATGCTCGATGAGTTTTTCTAATTGACGACTACTCGGCTGCATC Region 2 ForwardSEQ ID NO: 87 cdv3 HomologyCCTATGGAAAAACGCCAGCAACGCGCTTCAAGATGATCTGAGCTGAG Region 2 ReverseSEQ ID NO: 88 Kanamycin Cassette GGGAAAGCCACGTTGTGTCTC SEQ ID NO: 89Forward Kanamycin Cassette TTAGAAAAACTCATCGAGCATC SEQ ID NO: 90 Reverse

Additionally, all constructs contained flanking DNA from 900 to 1500 bpin length upstream and downstream of the targeted insertion site toallow homologous recombination with genomic sites. In some cases,deletion constructs for min components were designed to fully replacethe coding sequence (CDS) with a selectable marker (ΔminC and ΔdivIVA).In the case of the MinD and MinE knockouts, the MinD and MinE constructswere contained in a Ferredoxin-like operon. Hence, ΔMinD and ΔminEstrains were generated by synthesizing a gBlock (IDT DNA) thatconcatenated the operon, thereby removing either the MinD or MinE codingregion from the operon, and placing the resistance cassette downstreamto minimize operon disruption. The development of these constructs isillustrated in FIG. 1F.

To explore the effects of altered Min activity on cell shape,cyanobacterial strains were generated with an additional integrated copyof minC, minD, minE, and cdv3 under the control of riboregulators usingan inducible promoter that is turned on by the riboresponse regulator,theophylline, but that is tightly off in the absence of theophylline(Yoichi et al., Plant and Cell Physiology 54(10): 1724-1735 (2013)).Theophylline is an inexpensive commodity chemical that is generallyregarded as non-toxic and is therefore a feasible inducer in scaledcultivation.

Generation of MinC/D/E, Cdv3 and DivIVA overproduction strains, as wellas RS::mNG-MinC and RS::mNG-MinD fluorescent strains, was performed byinsertion of the constructs into Neutral Site 2, a genomically neutrallocus in S. elongatus, with an attached 5′ riboswitch (RS) expressedfrom the Ptrc promoter (FIG. 1F). In some constructs, native Cdv3,DivIVA and MinC were fluorescently tagged by insertion of mNeonGreen(mNG) into the native genomic locus by genetic recombination (Clerico etal., Methods Mol. Biol. 362, 155-171 (2007)). Integration was verifiedby PCR. Special attention was given to the insertion of the selectablemarker so as to minimize off-target effects in gene expression fromread-through transcription potentially initiated the resistance marker'spromoter (FIG. 1F).

Culture Conditions & Transformations

Cultures of S. elongatus were grown in 125 mL baffled flasks (Corning)containing 50 ml BG-11 medium (SIGMA) buffered with 1 g/L HEPES, pH 8.3.Flasks were cultured in a Multitron II (atrbiotech.com) incubationsystem with settings: 80 μmol m⁻² s⁻¹ light intensity, 32° C., 2% CO₂,shaking at 130 RPM unless otherwise stated. Cloning of plasmids wasperformed in E. coli DH5α chemically competent cells (Invitrogen). Allcyanobacterial transformations were performed as described by Clerico etal. (Methods Mol. Biol. 362: 155-171 (2007). Cells were plated on BG-11agar with either 12.5 μg ml⁻¹ kanamycin (overexpression, native andriboswitch strains) or 25 μg ml⁻¹ spectinomycin (deletion strains).Single colonies were picked into 96-well plates containing 300 μl ofBG-11 with identical antibiotic concentrations and cultures wereverified for complete gene replacement via PCR. Antibioticsupplementation was removed after complete gene replacement or knockoutwas verified.

Complete gene replacements were obtained for minC, minD, cdv3 andDivIVA.

Immunofluorescence Staining of FtsZ in Deletion and OverexpressionStrains

MinCDE and Cdv3 overexpression strains were inoculated into flaskscontaining 50 mL BG-11 and 2 mM theophylline. The cultures wereback-diluted with BG-11 and 2 mM theophylline to OD₇₅₀=0.2 whenevercultures reached OD₇₅₀≥0.7 to prevent artifacts in cell morphology dueto self-shading. The cells were incubated 72 hours before fixation.Extreme filamentation was observed in DivIVA overexpression strainsinduced for more than 5 days. Two mL of cells were fixed with 500 μl of2.5% glutaraldehyde/2.5% paraformaldehyde in 0.1M sodium cacodylatebuffer (pH 7.4) (Electron Microscopy Sciences) for 30 minutes at roomtemperature and washed with PBS+0.01% Tween-20. After treatment with0.05% Triton X-100 and 0.01% Tween-20 in PBS for 15 min, the cells werepermeabilized for 30 min at 37° C. with 20 μg ml⁻¹ lysozyme dissolved inTris-HCl, pH 7.5, 10 mM EDTA, washed, then blocked with 5% bovine serumalbumin (Sigma-Aldrich) in PBS (blocking buffer) for 1 hour. Cells wereincubated overnight at 4° C. with anti-Anabaena FtsZ antibodies(Agrisera Antibodies) diluted 1:250 in blocking buffer. Secondarystaining was conducted with 1:1000 goat anti-rabbit IgG Alexa Fluor 488(Life Technologies) in blocking buffer.

Fluorescence Microscopy

All live-cell microscopy was performed using exponentially growingcells. Images were captured using a Zeiss Axio Observer A1 microscope(100×, 1.46 NA) with an Axiocam ICc5 camera. Cell length measurementsfor all deletion, overexpression and native fluorescently tagged strainswere performed with live cells using manual tools in Zeiss Zen software.To induce translation of RS::mNG-MinC, cells were incubated for 30 minwith 100 μM theophylline before imaging. To induce translation ofRS::mNG-MinD, cells were incubated in 2 mM theophylline for 2 h. Lowerinduction and incubation times were used for RS::mNG-MinC imaging ofoscillation because increased induction could result in relativelydiffuse mNG-MinC signals, presumably due to over-saturation of MinDbinding sites. Two mL of culture was spun down at 5,000 g for 30 sec andmounted on glass slides containing a square 2% agarose+BG-11 pad.

Transmission Electron Microscopy

A wild-type culture of S. elongatus was grown to OD₇₅₀=0.7 in BG-11.Cells were pelleted and fixed for 30 min with 2.5% paraformaldehyde/2.5%glutaraldehyde in 0.1M sodium cacodylate buffer (pH 7.4), suspended in2% agarose and cut into 1 mm cubes. Following three washes with 0.1 Msodium cacodylate buffer, cells were suspended in 1% osmiumtetroxide/1.5% potassium ferrocyanide, microwaved in a MS-9000Laboratory Microwave Oven (Electron Microscopy Science) for 3 min, andwashed three times with HPLC-quality water. Cells were then suspended in1% uranyl acetate and microwaved for 2 minutes, decanted, and washedthree times with HPLC-quality water. Cells were dehydrated in increasingacetone series (2 min at 25° C.) and then embedded in Spurr's resin (25%increments for 10 minutes each at 25° C.). Thin sections of ˜70 nm wereobtained using an MYX ultramicrotome (RMC Products), post-fixed with 6%uranyl acetate and Reynolds lead citrate, and visualized on a JEM 100CXII transmission electron microscope (JEOL) equipped with an OriusSC200-830 CCD camera (Gatan).

Cyanobacterial Cell Sedimentation and Lysis Quantification

Cyanobacterial cells with a genomically-integrated copy of cdv3 or minEtagged with the fluorophore mTurquoise and driven by a theophyllineinducible riboswitch were expressed as described above. The specificconcentration of theophylline used, and length of time for the inductionwere as described in the figures and figure legends. For FIG. 6,uninduced or induced cells were suspended into 25 mL graduated cylindersand time-lapse images were captured using a standalone Nikkon Cameraevery 10 minutes over >100 hours. Resulting images were processed viaMATLAB software to convert the still images into a heatmap of celldensity as a function of height of the cylinder (FIG. 6B). Separately, 2mL of uninduced or induced cells (as indicated) were subjected to mildcentrifugation forces through the use of a benchtop centrifuge (accuSpin17 Fischer).

The same strains were passed through a Cell Disrupter (Constant Systems)with an injection volume that can be tuned from 0 kpsi to 40 kpsi. Cellswere subjected in two passes to the stated pressure (0, 4000 psi, or8000 psi). Flow through was collected and analyzed by flow cytometry onan Acuri C6 instrument (BD Biosciences) to determine the proportion ofintact and lysed cells. The indicated gates were used to discriminatebetween hyper-elongated cells (a result of Cdv3-OE) and normal lengthcells.

Example 2: Similarity of Min-Related Sequences

In two models of FtsZ regulation, MinCD is positioned in the cell byeither MinE or DivIVA (FIG. 1A). To gain insight into the conservationof Min components in cyanobacteria, several comparative analyses of S.elongatus Min-system proteins were performed. Alignments showed that S.elongatus MinD is highly conserved with its homologs in other bacteriaand chloroplasts. MinE exhibited lower sequence identity with the E.coli and Arabidopsis thaliana proteins, though conservation extendedover the length of the protein. Table 4 shows percent amino acididentity in pairwise comparisons between S. elongatus MinC(YP_401018.1), MinD (YP_399913.1), MinE (YP_399914.1) and Cdv3(YP_401023.1) and their homologs in E. coli (Ec) (MinC, NP_415694.1;MinD, NP_415693.1; MinE, NP_415692.1), B. subtilis (Bs) (MinC,NP_390678.1; MinD, NP_390677.1; DivIVA; NP_389425.1) and chloroplasts ofArabidopsis thaliana (At) (MinD, AED93246.1; MinE, NP_564964.1).

For example, an E. coli MinC (NP_415694.1) protein sequence is shownbelow as SEQ ID NO:91.

1 MSNTPIELKG SSFTLSVVHL HEAEPKVIHQ ALEDKIAQAP 41AFLKHAPVVL NVSALEDPVN WSAMHKAVSA TGLRVIGVSG 81CKDAQLKAEI EKMGLPILTE GKEKAPRPAP TPQAPAQNTT 121PVTKTRLIDT PVRSGQRIYA PQCDLIVTSH VSAGAELIAD 161GNIHVYGMMR GRALAGASGD RETQIFCTNL MAELVSIAGE 201YWLSDQIPAE FYGKAARLQL VENALTVQPL NAn example of a B. subtilis MinC protein sequence (NP_390678.1) is shownbelow as SEQ ID NO:92.

1 MKTKKQQYVT IKGTKNGLTL HLDDACSFDE LLDGLQNMLS 41IEQYTDGKGQ KISVHVKLGN RFLYKEQEEQ LTELIASKKD 81LFVHSIDSEV ITKKEAQQIR EEAEIISVSK IVRSGQVLQV 121KGDLLLIGDV NPGGTVRAGG NIFVLGSLKG IAHAGFNGNN 161QAVIAASEML PTQLRINHVL NRSPDHIQKG NEMECAYLDT 201DGNMVIERLQ HLAHLRPDLT RLEGGMA comparison of Min protein sequences from E. coli, Bacillus subtilis,and Arabidopsis thaliana is shown below.

TABLE 4 Percent Amino Acid Sequence Identity of Min Proteins from E.coli, Bacillus subtilis, and Arabidopsis thaliana E. coli B. subtilis A.thaliana MinC 20.8% 27.1% N/A MinD 46.1% 49.8% 53.0% MinE 27.3% N/A32.2%

An alignment of S. elongatus (Se; SEQ ID NO:4), E. coli (Ec; SEQ IDNO:91) and B. subtilis (Bs; SEQ ID NO:92) MinC sequences is shown below.

Se MSDVDASTPSAEEAIAPDIDSDSDAAVETPAAEPAIAPPIQLEAEGDRWWLRLPSAPPVG Ec.....................................................MSNTPIE Bs............................................................ SeQEANADGLTWLDLQQSLQQLLQGQENFWDAGAE L H L FADSWLLDGRQ L E....W.. L SQQ EcLKGSSFTLSVVHLHEAEPKVIHQALEDKIAQAP A F L KHAPVVLNVSA L EDPVNWSA M HKA Bs................MKTKKQQYVTIKGTKNG L T L HLDDACSFDEL L DGLQNMLS I EQY SeLARVDL KL TRIT.TQRRQTAVAAVSLGLS I ......EQPITQADPWQRKTST...SPIAA EcVSATGL RV IGVSGCKDAQLKAEIEKMGLPILTEGKEKAPRPAPTPQAPAQNT...TPVTK Bs TDGKGQKI SVHVKLGNRFLYKEQEEQLTE L IASKKDLFVHSIDSEVITKKEAQQIREEAE SePLYLKRTLRSGAEV.RHNGSVIVVGDVNPGSSIVASGDILVWGNLRGIAHAGAAGNSDAT EcTRLIDTPVRSGQRIYAPQCDLIVTSHVSAGAELIADGNIHVYGMMRGRALAGASGDRETQ BsIISVSKIVRSGQVLQVKGDLLLI.GDVNPGGTVRAGGNIFVLGSLKGIAHAGFNGNNQAV SeIFALSLAATQLRIGDRLARLPSSQAAGYPETA..QVIDGQIQIRRADPGGK......... EcIFCTNLMAELVSIAGEYWLSDQIPAEFYGKAARLQLVENALTVQPLN............. BsIAASEMLPTQLRINHVLNRSPDHIQKGNEMECAYLDTDGNMVIERLQHLAHLRPDLTRLE Se ... Ec... Bs GGM

An example of an E. coli MinD protein sequence (NCBI accession numberNP_415693.1) is provided below as SEQ ID NO:93.

1 MARIIVVTSG KGGVGKTTSS AAIATGLAQK GKKTVVIDFD 41IGLRNLDLIM GCERRVVYDF VNVIQGDATL NQALIKDKRT 81ENLYILPASQ TRDKDALTRE GVAKVLDDLK AMDFEFIVCD 121SPAGIETGAL MALYFADEAI ITTNPEVSSV RDSDRILGIL 161ASKSRRAENG EEPIKEHLLL TRYNPGRVSR GDMLSMEDVL 201EILRIKLVGV IPEDQSVLRA SNQGEPVILD INADAGKAYA 241DTVERLLGEE RPFRFIEEEK KGFLKRLFGG

An example of an Arabidopsis thaliana MinD protein sequence (NCBIaccession number AED93246.1) is provided below as SEQ ID NO:94.

1 MASLRLFSTN HQSLLLPSSL SQKTLISSPR FVNNPSRRSP 41IRSVLQFNRK PELAGETPRI VVITSGKGGV GKTTTTANVG 81LSLARYGFSV VAIDADLGLR NLDLLLGLEN RVNYTCVEVI 121NGDCRLDQAL VRDKRWSNFE LLCISKPRSK LPMGFGGKAL 161EWLVDALKTR PEGSPDFIII DCPAGIDAGF ITAITPANEA 201VLVTTPDITA LRDADRVTGL LECDGIRDIK MIVNRVRTDM 241IKGEDMMSVL DVQEMLGLSL LGVIPEDSEV IRSTNRGFPL 281VLNKPPTLAG LAFEQAAWRL VEQDSMKAVM VEEEPKKRGF 321 FSFFGG

An example of a B. subtilis MinD protein sequence (NCBI accession numberNP_390677.1) is provided below as SEQ ID NO:95.

1 MGEAIVITSG KGGVGKTTTS ANLGTALAIL GKRVCLVDTD 41IGLRNLDVVM GLENRIIYDL VDVVEGRCKM HQALVKDKRF 81DDLLYLMPAA QTSDKTAVAP EQIKNMVQEL KQEFDYVIID 121CPAGIEQGYK NAVSGADKAI VVTTPEISAV RDADRIIGLL 161EQEENIEPPR LVVNRIRNHL MKNGDTMDID EIVQHLSIDL 201LGIVADDDEV IKASNHGEPI AMDPKNRASI AYRNIARRIL 241GESVPLQVLE EQNKGMMAKI KSFFGVRS

An alignment of S. elongatus (Se; SEQ ID NO:14), E. coli (Ec; SEQ IDNO:93). Arabidopsis thaliana (At; SEQ ID NO:94) and B. subtilis (Bs; SEQID NO:95) MinD sequences is shown below.

Se M S RVIVVTSGKGGVGKTTSSANLG MA LA QL GKRLVLID A DFGLRNLDLLLGLENRIVY TAEc M A RIIVVTSGKGGVGKTTSSAAIA TG LA QK GKKTVVID F DIGLRNLDLIMGCERRVVY DFAt T P RIVVITSGKGGVGKTTTTANVG LS LA RY GFSVVAID A DLGLRNLDLLLGLENRVNY TCBs M G EAIVITSGKGGVGKTTTSANLG TA LA IL GKRVCLVD T DIGLRNLDVVMGLENRIIY DL         ---------          P-loop Walker A Se QDVL A G N CRL E QALVKDKRQP N . L C LLPA A NNR M K ..ES V T P QQ M EQ LV TL LD ....GQF EcVNVIQGDATLNQALIKDKRTEN.LYILPASQTRDK..DALTREGVAKVLDDLKA...MDF AtVEVINGDCRLDQALVRDKRWSN.FELLCISKPRSKLPMGFGGKALEWLVDALKTRPEGSP BsVDVVEGRCKMHQALVKDKRFDDLLYLMPAAQTSDK..TAVAPEQIKNMVQELKQ....EF SeDVILIDSPAGIE A GF Q NAI AA A R EAVIVTTPEIAAVRDADRVIGLLE A......H GI TE IEc EFIVCDSPAGIETGALMALYFADEAIITTNPEVSSVRDSDRILGILASKSRRAENGEEPI AtDFIIIDCPAGIDAGFITAITPANEAVLVTTPDITALRDADRVTGLLEC......DGIRDI BsDYVIIDCPAGIE QGYKNAVSGADKAIVVTTPEISAVRDADRIIGLLEQ.....EENIEPP      -----     SwitchII Se R .. LILNRLR PA MVK AN DMMSVEDV Q EIL A I P LVGIIPDD EQVII S TNRGEPLVL AEAP S EcKEHLLLTRYNPGRVSRGDMLSMEDVLEILRIKLVGVIPEDQSVLRASNQGEPVILDINAD AtK..MIVNRVRTDMIKGEDMMSVLDVQEMLGLSLLGVIPEDSEVIRSTNRGFPLVLNKPPT BsR..LVVNRIRNHLMKNGDTMDIDEIVQHLSIDLLGIVADDDEVIKASNHGEPIAMDPK.N                                               |                                             N222 Se L A AK AF I NVA RRLSGE S..IDFLN LEE PQ SGVL ..S KIRRI LNKKIL Ec.AGKAYADTVERLLGEE..RPFRFIEEEKKGFL..KRLFGG...... AtLAGLAFEQAAWRLVEQDSMKAVMVEEEPKKRGF..FSFFGG...... BsRASIAYRNIARRILGES..VPLQVLEEQN KGMMAKIKSF FGVRS...                              Membrane                              Targeting                              Sequence

An example of an E. coli MinE protein sequence (NCBI accession numberNP_415692.1) is shown below as SEQ ID NO:96.

1 MALLDFFLSR KKNTANIAKE RLQIIVAERR RSDAEPHYLP 41QLRKDILEVI CKYVQIDPEM VTVQLEQKDG DISILELNVT 81 LPEAEELK

An example of an Arabidopsis thaliana MinE protein sequence (NCBIaccession number NP_564964.1) is shown below as SEQ ID NO:97.

1 MAMSSGTLRI SATLVSPYHH HHRNRLSLPS SSSKVDFTGF 41ISNGVNSLET QKCTPGLAIS RENTRGQVKV LARNTGDYEL 81SPSPAEQEIE SFLYNAINMG FFDRLNLAWK IIFPSHASRR 121SSNARIAKQR LKMILFSDRC DVSDEAKRKI VNNIIHALSD 161FVEIESEEKV QLNVSTDGDL GTIYSVTVPV RRVKPEYQDV 201DEAGTITNVE YKDTRDGSVD VRFDFYVPE

An alignment of S. elongatus (Se; SEQ ID NO:23), E. coli (Ec; SEQ IDNO:96), and Arabidopsis thaliana (At; SEQ ID NO:97) MinE sequences isshown below.

Se ............................................................ Ec............................................................ AtSSSSKVDFTGFISNGVNSLETQKCTPGLAISRENTRGQVKVLARNTGDYELSPSPAEQEI Se..................MLADLFERLFP R QQA S RDT VK Q RL KLVLAH.D R A DL SPELLQEc ....................MALLDFFLS R KKN T ANI AK E RL QIIVAERR R S DAEPHYLP At ESFLYNAINMGFFDRLNLAWKIIFPSHAS R RSS N ARI AK Q RL KMILFS.D R CDV SDEAKR                       ------            -                 Membrane Targeting    R21                      Sequence                                  -------------------                                  MinD Contact Helix Se K M RQE IL E VVSR YV E LD S E G...MEL S L E N D QRVTALV ANLP . I RR VK PATAEG...... EcQ L RKD IL E VI CK YV Q ID P E MVTVQLE Q K D G D ISILELN VTLP E A EE LK............ At K I VNN II H AL SD FV E IE S E EKVQLNV S T D G D LG.TIYSVTVP . V RR VK PEYQDVDEAGTI Se ....................... Ec....................... At TNVEYKDTRDGSVDVRFDFYVPE

A further comparison of S. elongatus (Selong; SEQ ID NO:98) and E. coliK12 substrain MG1655 (E coli; SEQ ID NO:99) MinE homologs is shownbelow, where asterisks below the sequences indicates amino acid sequenceidentity.

MinE: 32.8% identity in 64 residues overlap; Score: 100.0; Gapfrequency: 1.6%

Ecoli 3 LLDFFLSRKKNTANIAKERLQIIVAERRRSDAEPHYLPQLRKDILEVICKYVQIDPEMVTSelong 5 LFERLFPRQQASRDTVKQRLKLVLAHDR-ADLSPELLQKMRQEILEVVSRYVELDSEGME*      *        * **    *  *  *  *  *   *  ****   **  * * Ecoli 63 VQLESelong 64 LSLE   **

MinC proteins in bacteria are generally conserved primarily in a regionnear their C-termini that mediates MinC dimerization and interactionwith MinD (Hu & Lutkenhaus, 2000), and this region was also conserved inS. elongatus MinC. Unlike in E. coli, where MinC, MinD and MinE are allencoded by the minB operon (de Boer et al, E. coli. Cell 56: 641-649(1989)), genomic analysis showed that S. elongatus minD and minE residein an operon with a ferredoxin-like gene of unknown function, while minCwas located at a distant chromosomal region with its own promoter (FIG.1B).

S. elongatus Min homologs were analyzed in greater detail using Phyre2(Mezulis et al, Nature Protocols 10: 845-858 (2015)) to look for proteinfeatures via structural prediction. The results indicated that the Minproteins possessed secondary and tertiary structures that are highlyconserved with those in the E. coli MinC, MinD and MinE crystalstructures (FIG. 1C-1E, left panels). Key domains previously shown tohave a role in Min protein function and dynamics in E. coli wereidentified in all three predicted S. elongatus structures. For example,MinC was predicted to bear multiple N-terminal alpha helices thatfunction in binding to and depolymerizing FtsZ in E. coli, andC-terminal β-sheets important for homodimerization (FIG. 1C) (Hu &Lutkenhaus, Annu. Rev. Biochem. 76: 539-562 (2000)). Additionally, MinCpossessed several conserved glycine residues involved in MinC functionin E. coli, including G161 near the A-surface (G200 in S. elongatus)that can be involved in homodimerization; and G135, G154 and G171 nearthe B-C surface (G175, G193 and G210 in S. elongatus) that can beinvolved in interaction with MinD (Ramirez-Arcos et al, J. Bacteriol.186: 2841-2855 (2004). MinD possessed a highly conserved N-terminalWalker A-type ATPase domain, Switch I and Switch II domains for bindingMinC, and key residues L48, E53, and N222 (L48, E53 and N213 in S.elongatus) that are involved in interaction with MinE (Szeto et al,Proc. Natl. Acad. Sci. U.S.A. 99: 15693-15698 (2004)). Additionally,MinE possessed the R21 residue (R23 in S. elongatus), which is involvedin hydrogen bond formation with E53 of MinD, and a highly conserved β1strand concealed within a contact helix that's inserted at the MinDdimer interface, stabilized as an α-helix and involved in thestimulation of ATPase activity (FIG. 1E) (Park et al, Cell 146: 396-407(2011)). Likewise, both MinD and MinE were predicted to possess thenecessary structures for membrane-binding, which included a C-terminalamphipathic helix on MinD (FIG. 1D) and a N-terminal amphipathic helixon MinE (FIG. 1E) (Hsieh et al, Mol. Microbiol. 75: 499-512 (2010)). Thehydrophobic residues of these helices typically mediate transientinteractions with the non-polar environment underneath the membraneinterface and facilitate binding of E. coli MinD and MinE tophospholipid membranes in vivo and in vitro (Loose et al, System. Annu.Rev. Biophys. 40: 315-336 (2011b)).

FIG. 1F is a schematic illustration of construct designs. In S.elongatus, MinC and DivIVA are expressed individually, whereas MinD andMinE are in the same operon with a putative ferredoxin-like gene (blue)of unknown function. In mNG-MinC, MinC was codon-optimized (CO) toincrease transformation frequency. FIG. 1G shows PCR verification of Mingene deletions.

One example of a B. subtilis DivIVA sequence has NCBI accession numberAQR85736.1, shown below as SEQ ID NO:100.

1 MPLTPNDIHN KTFTKSFRGY DEDEVNEFLA QVRKDYEIVL 41RKKTELEAKV NELDERIGHF ANIEETLNKS ILVAQEAAED 81VKRNSQKEAK LIVREAEKNA DRIINESLSK SRKIAMEIEE 121LKKQSKVFRT RFQMLIEAQL DLLKNDDWDH LLEYEVDAVF 161 EEKE

Example 3: Cyanobacterial Min Homologs Regulate Cell Size and Z-RingAssembly

The data described in Example 2 indicates that S. elongatus possesses aMin system. The inventors' screen for division-related factors in S.elongatus (Miyagishima et al., Mol Microbiol 56:126-43 (2005)) andpreliminary studies in the spherical-shaped cyanobacterium Synechocystissp. (Mazouni et al., Mol Microbiol 52:1145-58 (2004)) have providedevidence that four Min homologs from Synechocystis sp., Bacillussubtilis, E. coli, and S. elongatus function in cell division. However,there has been no systematic analysis of altered Min system expressionor dynamics in cyanobacteria. Additionally, the presence of thethylakoid membrane network in cyanobacteria could influence Min systembehavior, as MinD, MinE, and DivIVA all transiently associate withmembranes in other bacteria through relatively small, nonpolar proteindomains.

To investigate the similarities and differences in function of thecyanobacterial Min system, minC, minD, minE and divIVA deletion (Δ) andoverexpression (OE) strains were generated as explained in Example 1 andas illustrated in FIG. 1F-1G. These minC, minD, minE and divIVA deletionand overexpression strains were analyzed for defects in morphology andFtsZ organization.

In wild-type (WT) cells, cell sizes fell within a narrow range of about1.7-4.5 μm (mean cell length 3.10±0.66 μm; FIG. 2A-2B). The Z rings inwild type cells detected by immunofluorescence labeling were alwayspositioned at the midcell (FIG. 2A-2B).

In contrast, ΔminC deletion strains exhibited a broader distribution oflarge and small cells with Z rings that were frequently mispositionednear the poles (FIG. 2A-2C). MinC-OE overexpression strains exhibited ahigh proportion of elongated cells with Z rings displaced from midcell,but generally not adjacent to cell poles (FIG. 2A blue profile for minCrelative to the WT (red) distribution). Many cells contained faint FtsZspots or rings, suggesting inhibited FtsZ polymerization (FIG. 2B-2C). Abroad distribution of large and small cells were observed in both S.elongatus ΔminD and MinD-OE strains was observed (FIG. 2A). The S.elongatus ΔminD and MinD-OE strains also exhibited mispositioned polar Zrings (FIG. 2B-2C). These results demonstrate that MinC and MinDfunction as regulators of both assembly and positioning of the Z ring inS. elongatus, consistent with their roles in E. coli.

Because the cellular architecture of cyanobacteria could potentiallyinterfere with the MinE-driven oscillations that are required toposition MinCD in E. coli, cyanobacterial minE mutants were evaluated toascertain whether they would display Z-ring assembly and positioningdefects. MinE-OE overexpression strains were elongated (FIG. 2A), butexhibited well-defined, mispositioned Z rings (FIG. 2B-2C), a resulthighly similar to MinE overexpression in E. coli (de Boer et al, E.coli. Cell 56: 641-649 (1989)). A fully-penetrant deletion of MinEacross all chromosomal copies was not obtained, indicating that deletionof MinE is lethal (FIG. 1G). However, meroploid S. elongatus ΔminE cellswere elongated (FIG. 2A) and possessed a unique pattern of disorganizedFtsZ structures throughout the cell, which occasionally formed anextended helix-like pattern (FIG. 2B-2C). Note that in E. coli, knockoutof minE is lethal and leads to a formation of MinCD polymers along thelength of the plasma membrane (de Boer et al., Cell 56: 641-649 (1989);Ghosal et al., Nature Communications 5: 1-11 (2014)).

Example 4: Theophylline Induction of Cell Growth and MinC and Cdv3Expression

The Example illustrates induction of cyanobacterial cell growth as wellas expression of MinC and Cdv3 expression.

Methods

mTurquoise-tagged fusions of Min factors (Cdv3-mTurq, mTurq-MinE, andmTurq-MinC) were expressed under the control of atheophylline-responsive riboswitch. Cells were exposed to increasingconcentrations of theophylline (0,200 μM, 800 μM, or 2000 μM). Averagefluorescence intensity per pixel was quantified in mTurq-MinC orCdv3-mTurq expressing S. elongatus cells induced with suchconcentrations of Theophylline.

FIGS. 2E-2F, validate that increasing theophylline concentrationsincrease the amount of the gene (MinC and Cdv3) that is expressed underthe riboswitch element. The relationship between the inducerconcentration and the expression of the gene is direct and linear.

FIG. 2G illustrates the cyanobacterial growth rate in response toincreasing theophylline inducer. Wild-type S. elongatus was incubatedwith increasing concentrations of theophylline and monitored for growthover 24 hours by optical density at 750 nm (OD₇₅₀). Doubling time wascalculated for n≥4 independent day experiments. Error bars representstandard deviation and the p value for the only significant (p<0.05)change in doubling time is denoted, as determined from pairwise unequalvariances t-tests. As illustrated in FIG. 2G, the growth (doubling time)of cyanobacteria was substantially unaffected by differentconcentrations of theophylline.

Hence, the addition of theophylline can induce expression of theinducible transgenes described herein without affected the growth of thecyanobacterial host cell lines.

Example 5: MinCD Oscillate from Pole-to-Pole in S. elongatus

In E. coli FtsZ assembles at the plasma membrane, which isfreely-accessible to the cytosolic pool of oscillating MinCDE molecules(Lutkenhaus, Annu. Rev. Biochem. 76: 539-562 (2007)). However theinfluence of cyanobacterial internal membranes on the dynamics of Minproteins is unknown. While perforations in thylakoid membranes couldfacilitate sufficient diffusion of MinCDE across thylakoid layers tosupport emergence of MinCDE oscillations, thylakoid membranes could alsopose a steric barrier that limits MinCDE access to the plasma membrane.

To gain insight into how Min dynamics contribute to Z-ring positioningin S. elongatus, N-terminal mNeonGreen (mNG) fusions were generatedwhere mNG was fused to both MinC and MinD, and where these fusionproteins were expressed from a synthetic riboswitch at a genomic neutralsite (FIG. 3A-3C). The fluorescent reporter mNG was chosen for itsbright, photostable and monomeric properties, as well as itsyellow-shifted excitation, highly reducing the autofluorescencegenerated from photosynthetic pigments in S. elongatus during imaging.In some cases, the endogenous (native) Min proteins were deleted toidentify the effects of induced Min protein expression (FIG. 3A-3C).

Time-lapse imaging revealed that both mNG-MinC and mNG-MinD oscillatedfrom pole to pole (FIG. 3E). FIG. 3D graphically illustrates that theperiodicity of mNG-MinC increases proportionally with cell length (n=10cells per cell length). However, N- or C-terminal fusions to MinE werenot obtained that were functional in S. elongatus.

Experiments were then performed to verify and characterize Minoscillations in a reporter strain that would mimic endogenous expressionlevels and minimize off-target expression effects. Modification of MinDor MinE activity can alter the periodicity of oscillations in E. coli(Lutkenhaus, 2007), but MinC is a “passenger protein” in the MinDEoscillation and is not in a larger operon in S. elongatus. Therefore,the chromosomal minC gene was completely replaced with an mNG-minCreporter fusion expressed from the native promoter at the endogenouschromosomal locus (FIG. 3A). In these strains, mNG-MinC oscillated frompole-to-pole (FIG. 3D-3E). Cell lengths and growth rates were unchangedin the native mNG-minC strain relative to wild type, indicating thefusion protein possessed WT functionally.

The mNG-MinC reporter transgene included the wild type MinC codingregion linked to the mNeonGreen (mNG) fluorescent reporter fusionpartner. This native MinC reporter oscillated with a periodicity thatwas about two times (2×) slower than in equivalently sized E. colicells. The periodicity increased linearly as a function of increasingcell length during growth (about 10 s for each additional 1 μm of celllength) (FIG. 3D), and paused at each pole for about 10 seconds.

To confirm a role for MinDE in oscillation of MinC, ΔminD and ΔminEmutants were generated in this native mNG-MinC reporter line. Consistentwith a role for MinD in recruitment of MinC to membranes, mNG-MinC wascompletely diffuse in ΔminD cells (FIG. 3F-3G). Conversely, mNG-MinCformed helical structures in incomplete minE deletion strains (FIG.3H-3I), reminiscent of MinCD copolymer formation in E. coli and FtsZstaining in S. elongatus ΔminE cells (FIG. 2B).

Example 6: Cdv3 Recruits MinCD to the Z Ring and is Needed forProvisioning a Functional Divisome

During the in vivo imaging experiments, a subpopulation of mNG-MinC didnot oscillate, but formed a ring-like structure at midcell. This midcelllocalization could not be readily explained from the E. coli model ofemergent MinCDE dynamics. The pool of mNG-MinC at the midcell wasrapidly photobleached during time-lapse imaging, and after bleaching thesignal did not recover on the same time scales (i.e. minutes) that MinCDwere observed to complete an oscillation (FIG. 3E). These observationsindicated that the midcell subpopulation of MinC may not readily berecycled and might be localized through an independent mechanism fromMinE-driven oscillations. However, the localization of thissubpopulation of MinC does resemble that observed in actively dividingB. subtilis cells, where DivIVA recruits MinCD to midcell through MinJ.

Cyanobacteria may possess a DivIVA-like protein called Cdv3, which mightalso function to position MinCD (Nakanishi et al., Commun Integr Biol 2:400-402 (2009); Miyagishima et al., Mol. Microbiol. 56: 126-143 (2005)).However, Cdv3 shares low primary sequence identity with DivIVA of B.subtilis (FIG. 4A). Furthermore, while divIVA is commonly locateddownstream of the well-characterized division and cell wall (dcw)cluster in gram-positive bacteria, in S. elongatus, cdv3 does notcluster with cell wall or division genes but instead overlaps with thecoding sequence for coaD, a gene important for Coenzyme A synthesis(FIG. 4A). Structural modeling of B. subtilis DivIVA based on separatelycrystallized N- and C-terminal domains suggested an extended tetramerconsisting predominantly of antiparallel coiled coils (Oliva et al, EMBOJ. 29: 1988-2001 (2010)). While Cdv3 could not be modeled onto thisstructure, JPred4 analysis indicated that there may similar coiled-coilstructures spanning the majority of B. subtilis DivIVA and S. elongatusCdv3. Furthermore, Delta-Blast identified the presence of a sharedDivIVA domain in both proteins and the inventors identified conservationat residues V25 and L29 (V46 and L50 in S. elongatus) that can beimportant for DivIVA function in B. subtilis (Oliva et al. EMBO J 2010;29:1988-2001 (2010) (FIG. 4B). However, Cdv3 does not have conservationof residues (S16, F17, R18, G19, Y20) reported to be required forsensing and binding of DivIVA to negatively-curved membrane regions(FIG. 4B). An alignment of S. elongatus (Se; SEQ ID NO:103) Cdv3 and B.subtilis (Bs; SEQ ID NO:104) DivIVA sequences is shown below.

Se MTQAQSLDVLNLLEQLEESVLDGTRVPLSGRILVRENDLLDLLDDVRAGLPAAIQQAQQI Bs....................MPLTPNDIHNKTFTKSFRGYDE.DEVNEFLAQVRKDYEIV                                -----                                Crossed Loops SeLERQAQILADAQQQAQAIVAQAQQE....RALLIDQNS...IRLQAERDAQQLRQTLQQE BsLRKTELEAKVNELDERIGHFANIEETLNKSILVAQEAAEDVKRNSQKEAKLIVREAEKN SeCDALRQQAIAEATQVRGEAQQFQLQVRQETDSLRQQTQAEIEQLRSQTQQQLSEQRQRIL BsADRIINESLSKSRKIAMEIEELKKQSKVFRTRFQMLIEAQLDLLKNDDWDHLLEYEVDAV SeVECEELRRGADSYADQVLRDMEQRLTQMMQIIRNGRQALNLSENTPPPAPRRRSR BsFEEKE..................................................

Additionally, Cdv3 lacked C-terminal peptides required for interactionof DivIVA with MinJ and RacA (van Baarle et al, 2013), which are notpresent in cyanobacteria. Therefore, Cdv3 possesses partial conservationto DivIVA, but it has been unclear what function it may serve given thefact that the MinCDE oscillations in vivo described herein arepotentially sufficient to confine FtsZ polymerization to the midcell.

The role of Cdv3 and DivIVA in cell division was investigated bygenerating deletion, overexpression, and reporter lines (FIGS. 1F and3C). First, a reporter strain was generated in which the native cdv3gene was completely replaced with a C-terminal mNG fusion. Expression ofsuch a Cdv3-mNG transgene concentrates Cdv3 to the midzone of the cellin a ring-like structure. This localization is observed prior to othersigns of cell constriction and persists throughout cytokinesis (FIG.4C). The Cdv3-mNG strains possessed wild-type growth rates and celllengths, indicating the Cdv3-mNG fusion maintained functionality.

In contrast, Δcdv3 strains exhibited a highly elongated morphology (FIG.4D-4E). FtsZ localization in such Δcdv3 strains was unlike that in ΔminEand MinE-OE strains; FtsZ was localized in regularly-spaced Z ringsthroughout the cell (compare FIGS. 4F and 2B). Furthermore,overexpression of Cdv3 arrested division and resulted inhyper-elongation (FIG. 2C-2D) with FtsZ localizing to irregularly spacedZ rings interspersed with disorganized FtsZ filaments (FIGS. 4F and 2C).Taken together, these results indicate that Cdv3 has a function inregulating Z-ring positioning and/or constriction that is not redundantwith MinE.

To ascertain if Cdv3 or other Min proteins have a role in recruiting themidzone-localized subpopulation of MinC, S. elongatus Min mutants weregenerated in the mNG-MinC fluorescent reporter line. The pool ofmidcell-localized mNG-MinC was abolished in ΔminD and Δcdv3 strains,indicative of roles for MinD and Cdv3 in the midcell recruitment of MinC(FIG. 3F-3G; FIG. 4D). Although the midcell localization of MinC wasdisrupted in filamentous Δcdv3 strains, these cells still exhibitedoscillatory waves of mNG-MinC (FIG. 4D, 4G). These results indicate thatboth Cdv3 and MinE spatially regulate Z-ring assembly by providingtopology to distinct pools of MinCD in cyanobacteria.

FIG. 4H illustrates that DivIVA (related to cdv3 in S. elongatus asdescribed herein) localization to division planes is independent ofother Min system regulators. DivIVA-mNG was imaged in ΔminC, ΔminD andΔminE backgrounds. Upon the deletion of minC, the DivIVA signal appearedat midcell. In ΔminD backgrounds, DivIVA localization appeared inring-like patterns that were often observed in multiple locations alongthe length of elongated cells, and where the ring-like structures werefrequently near cell poles (FIG. 4H). These localizations are consistentwith FtsZ staining in ΔminC and ΔminD cells, respectively.Interestingly, ΔminE cells displayed erratic DivIVA-mNG localization(FIG. 4H), where ring-like structures formed randomly in the cell (oftenat constricting sites presumed to be division planes), while alsoforming a helical pattern that was reminiscent of FtsZ patterning inΔminE cells. These patterns indicate that DivIVA and FtsZ co-localize inS. elongatus.

Example 7: Effects of Cdv3 Expression Upon FtsZ Ring Formation

This Example illustrates that Cdv3 overexpression can elongate cells,for example, by reducing the rate of formation of FtsZ rings andimpairing their capacity to constrict.

Methods

Expression of Cdv3 in riboswitch::Cdv3-mTurq strains was induced with400 μM theophylline and representative bright-field images from each dayfollowing induction were obtained.

Results

FIG. 4I shows images of immunolocalized FtsZ (yellow) in representativecells where Cdv3 expression was induced for the indicated number ofhours. As illustrated, formation of Z-rings was delayed in Cdv3-mTurq(blue) expressing lines (24 hr-OE), whereas cells of this size wouldnormally have at least one FtsZ ring. At later time points, in severelyelongated cells, multiple, mis-positioned Z-rings are evident (48-72hours post-induction), yet there is no clear indication of FtsZconstriction in such cells.

Example 8: Cell Size Modulation by MinC, MinD, MinE, and Cdv3

This Example illustrates that cell size can be modulated in a controlledmanner by regulated expression of MinC, MinD, MinE, and Cdv3.

Cyanobacterial cells that inducibly expressed MinC, MinD, MinE, or Cdv3were generated as described in Example 1 or 2, where these genes weretagged with the fluorescent reporter mTurquiose in order to verifyexpression and determine localization. No fluorescence was observed inany of the cell lines when theophylline was not added to the culture,but mTurquiose fluorescence was detected in a direct relationship to theamount of theophylline added (data not shown). The cells were culturedin concentrations of theophylline varying from 0 μM to 2 mM, and thedimensions of cells were measured after 24 hours of overexpression. Celllength measurements for overexpression strains were performed with livecells using manual tools in Zeiss Zen software.

FIG. 5A-5E illustrate cyanobacterial cell elongation when MinC, MinD,MinE, and/or Cdv3 proteins are overexpressed. FIG. 5A is a schematicdiagram of a cyanobacterial cell illustrating the locations of MinC,MinD, MinE, Cdv3, and FtsZ proteins, as well as the effect ofoverexpressing MinC protein on cell length. FIG. 5B graphicallyillustrates cell length upon inducing expression of MinC protein (leftpanel) and MinD protein (right panel) with increased amounts of theinducer (theophylline). As illustrated, greater concentrations of thetheophylline inducer lead to cyanobacterial populations with increasedmean cell lengths. FIG. 5C graphically illustrates cell length uponinducing expression of MinE protein (left panel) and Cdv3 protein (rightpanel) with increased amounts of the inducer (theophylline). Asillustrated, greater concentrations of the theophylline inducer lead tocyanobacterial populations with increased mean cell lengths.

MinC cells with MinC expression induced at the highest theophyllineconcentrations were elongated by about 20-fold, reaching average celllengths of 45 μm after 96 hours (FIG. 5D). These cells were hypervariable in length (FIG. 5D), in contrast to cells where MinC expressionwas induced at lower levels where a new steady-state cell length ofabout 2-3 fold larger than uninduced cells was obtained by 48 hoursafter induction.

Long-term overexpression of minE did not stably increase cell lengths(FIG. 5E, left panel). At later time points all cells that overexpressedMinE returned to a baseline length of about 3 μm (FIG. 5E, right panel).

By contrast, with any additional over-expression of Cdv3, Synechococcuselongatus cells elongated at an accelerating rate over time. Most cellsreached lengths greater than 100 μm after 3-4 days of induction (FIG.5E). Cell division was exquisitely sensitive to overexpression of Cdv3Similar elongation rates were observed regardless of the amount oftheophylline inducer. These data indicate that even minor changes inCdv3 activity can lead to near arrest of cell division and that cellgrowth is decoupled from division when Cdv3 is overexpressed.

FIG. 5F shows brightfield microscopy images of elongated cyanobacterialcells that have been induced to over-express Cdv3. The scale of theseimages was changed between the panels to illustrate the extremeelongation that is seen in these cells.

Example 9: Hyper-Elongated Cells are More Prone to Sediment

Cdv3 (DivIVA) expression was induced in cyanobacteria with the cdv3(divIVA) overexpression transgene. The effectiveness of gravitysedimentation of the elongated cells was monitored by observing the rateat which cells fell out of a water column (FIG. 6A). Cell sedimentationwas recorded over time to track the spontaneous settling via gravity anda direct correlation with the cell length and rapidity of sedimentationwas observed (FIG. 6A-6C). Sedimentation took place over several hourswithout added gravitational forces (FIG. 6A-6B). Sedimentation occurredfaster when additional gravitational forces were applied andsedimentation of Cdv3 (DivIVA) overexpressing cells was faster than MinEoverexpressing cells (FIG. 6C).

Example 10: Hyper-Elongated Cells are More Readily Lysed

Cdv3 (DivIVA) expression was induced in cyanobacteria with the cdv3(DivIVA) overexpression transgene. The vulnerability of elongated cellsto lysis by mechanical forces was evaluated by subjecting the cells totorsional/shear forces that are often employed to lyse cells forbioproduct recovery. Cell elongation increases the cell surface tovolume ratio. Cell elongation also increases the area over which cellscan be exposed to lysing agents. In addition, torsional forcesexperienced by an elongated cell under sheer stress are likely greater,barring other structural changes.

The differential susceptibility of elongated cells was examined bytracking populations of cyanobacterial cells through flow cytometry,before and after passage through a cell disrupter, as described inExample 1. As shown in FIG. 7A, the cell population exhibited anincrease in cell forward scatter and chlorophyll a autofluorescencefollowing induction of Cdv3 expression through the addition oftheophylline (400 μM). Such increased cell forward scatter andchlorophyll a autofluorescence correlated with increasing cell sizes(FIG. 5; FIG. 7A).

Populations of Cdv3-overexpressing cells were subjected to relativelymild pressures in a cell disrupter and examined for cell lysis throughflow cytometry (FIG. 7B). Significant decreases in the proportion ofelongated cells were observed following passage through the celldisrupter at the lowest pressure that could be programmed, and nearlycomplete lysis of the elongated population occurred at 8000 psi (FIG.7B-7D). In contrast, uninduced cells or Cdv3-overexpressing cells werenot significantly lysed at the lowest pressure tested, and were onlypartly disrupted at 4000 psi or at 8000 psi (FIG. 7C-7D).

Example 11: Hyperelongation of Cells by Overexpressing Cdv3 does notReduce Biomass Produced or Cell Mass Recovered

This Example shows that overexpression of Cdv3, which elongates cells,does not adversely affect the capacity of the cells to grow during theperiod of hyperelongation. Furthermore, the cells can still be collectedwithout loss of biomass to cell lysis.

As illustrated in the foregoing Examples, increasing the expressionlevel of various proteins (e.g., MinC, Cdv3) leads to increased celllength by arresting division. One concern is that, although such largercells may be easier to harvest/process, the cells may exhibit reducedproductivity during the elongation period due to the abnormal cell sizeor the cells could be damaged by the procedures used by the harvestingprocess. For example, if the cells become too sickly, if changes of thecell volume:surface area adversely impact photosynthesis, if theirmetabolism dramatically changes, or if their cell walls become weak, theyield of harvested cells may decline. This concern was addressed usingthe following procedures.

Methods

At time zero, Riboswitch::Cdv3-mTurq S. elongatus cultures wereback-diluted to OD₇₅₀=0.25. Theophylline was added to a finalconcentration of 400 μM to induce Cdv3-mTurq expression in some cultures(Cdv3-Induced: FIG. 7E, light grey bars), while no theophylline wasadded to negative controls (Uninduced: FIG. 7E, dark grey bars). Cellswere pelleted in a Sorvall SS-34 rotor for 10 minutes at 5000 rpm after36 or 60 hours of incubation (induction) with theophylline. Followingdesiccation of the cell pellets, dry cell biomass was measured.

Results

As illustrated in FIG. 7E, there is no significant reduction in theamount of cell biomass accumulated in hyperelongated cells generated byinducing overexpression of Cdv3 even when the cells were harvested bypelleting. The dry cell mass of negative controls (Uninduced: dark greybars in FIG. 7E) was about the same as the dry cell mass ofCdv3-expressing cells with Cdv-3 induced by theophylline (light greybars in FIG. 7E).

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All patents and publications referenced or mentioned herein areindicative of the levels of skill of those skilled in the art to whichthe invention pertains, and each such referenced patent or publicationis hereby specifically incorporated by reference to the same extent asif it had been incorporated by reference in its entirety individually orset forth herein in its entirety. Applicants reserve the right tophysically incorporate into this specification any and all materials andinformation from any such cited patents or publications.

The following statements are intended to describe and summarize variousembodiments of the invention according to the foregoing description inthe specification.

Statements:

-   -   1. A cyanobacterial population comprising cells with at least        one expression cassette comprising a promoter operably linked to        a nucleic acid segment encoding a MinC protein, MinD protein,        MinE protein, Cdv3 (DivIVA), FtsZ or Ftn2 protein; or a        combination of expression cassettes, each expression cassette        comprising a promoter operably linked to a nucleic acid segment        encoding a MinC protein, MinD protein, MinE protein, Cdv3        (DivIVA) protein, FtsZ protein, or Ftn2 protein.    -   2. The cyanobacterial population of statement 1, with a mean        cell length that is at least 150%, or at least 200%, or at least        250%, or at least 300%, or at least 500%, or at least 750%, or        at least 1000%, or at least 5000%, or at least 10000%, or at        least 15000%, or at least 20000% greater than a wild type        population of cyanobacteria of the same species.    -   3. The cyanobacterial population of statement 1, with a mean        cell length that is at least 15%, or at least 20%, or at least        25%, or at least 30%, or at least 35%, or at least 40%, or at        least 45%, or at least 50% less than the mean cell length of a        wild type population of cyanobacteria of the same species.    -   4. The cyanobacterial population of any of statements 1-3,        wherein each promoter is a constitutive promoter, inducible        promoter, regulated promoter, cell specific promoter, or        synthetic promoter.    -   5. The cyanobacterial population of any of statements 1-4,        wherein the promoter is active before or during log phase growth        of the cells in a culture or fermentation medium.    -   6. The cyanobacterial population of any of statements 1-4,        wherein the promoter is active at the end, or after, log phase        growth of the cells in a culture or fermentation medium.    -   7. The cyanobacterial population of any of statements 1-6,        comprising increased expression of a MinC, MinD, MinE, Cdv3        (DivIVA), FtsZ, or Ftn2 protein relative to a wild type        population of cyanobacteria of the same species.    -   8. The cyanobacterial population of any of statements 1-7,        wherein the MinC, MinD, MinE, Cdv3 (DivIVA), FtsZ, or Ftn2        protein is expressed at levels that are at least 15%, or at        least 20%, or at least 25%, or at least 30%, or at least 35%, or        at least 40%, or at least 45%, or at least 50% more than a wild        type population of cyanobacteria of the same species.    -   9. The cyanobacterial population of any of statements 1-8,        wherein the MinC polypeptide has at least 70%, or at least 75%,        or at least 80%, or at least 85%, or at least 90%, or at least        95%, or at least 97%, or at least 98%, or at least 99% sequence        identity to any of SEQ ID NOs:4, 6-9, or 10.    -   10. The cyanobacterial population of any of statements 1-9,        wherein the MinD polypeptide has at least 70%, or at least 75%,        or at least 80%, or at least 85%, or at least 90%, or at least        95%, or at least 97%, or at least 98%, or at least 99% sequence        identity to any of SEQ ID NOs:14, 15-18, or 19.    -   11. The cyanobacterial population of any of statements 1-10,        wherein the MinE polypeptide has at least 70%, or at least 75%,        or at least 80%, or at least 85%, or at least 90%, or at least        95%, or at least 97%, or at least 98%, or at least 99% sequence        identity to any of SEQ ID NOs:23, 25-31, or 32.    -   12. The cyanobacterial population of any of statements 1-11,        wherein the Cdv3 (DivIVA) polypeptide has at least 70%, or at        least 75%, or at least 80%, or at least 85%, or at least 90%, or        at least 95%, or at least 97%, or at least 98%, or at least 99%        sequence identity to any of SEQ ID NOs:33, 35-38, or 39.    -   13. The cyanobacterial population of any of statements 1-12,        wherein the Ftn2 polypeptide has at least 70%, or at least 75%,        or at least 80%, or at least 85%, or at least 90%, or at least        95%, or at least 97%, or at least 98%, or at least 99% sequence        identity to any of SEQ ID NO:45.    -   14. The cyanobacterial population of any of statements 1-13,        wherein the FtsZ polypeptide has at least 70%, or at least 75%,        or at least 80%, or at least 85%, or at least 90%, or at least        95%, or at least 97%, or at least 98%, or at least 99% sequence        identity to any of SEQ ID NOs:40, 42, 43, or 44.    -   15. The cyanobacterial population of any of statements 1-13,        wherein the population has a faster sedimentation rate than a        wild type cyanobacterial population of the same population.    -   16. The cyanobacterial population of any of statements 1-15,        wherein the extracellular or intracellular components expressed        by the cells are more easily (cheaply) obtained from the        population than from a wild type cyanobacterial population of        the same population.    -   17. The cyanobacterial population of any of statements 1-16,        wherein the population requires less sheer force for cell lysis        than a wild type cyanobacterial population of the same        population.    -   18. The cyanobacterial population of any of statements 1-17,        wherein the population is more buoyant than a wild type        cyanobacterial population of the same population.    -   19. The cyanobacterial population of any of statements 1-18,        wherein mixing the population requires less energy than a wild        type cyanobacterial population of the same population.    -   20. The cyanobacterial population of any of statements 1-19,        wherein intracellular components expressed within the cells are        more easily obtained from the population than from a wild type        cyanobacterial population of the same population.    -   21. A cyanobacterial population comprising mutant cyanobacterial        cells comprising a mutation in a MinC gene encoding a MinC        polypeptide, a MinD gene encoding a MinD polypeptide, a MinE        gene encoding a MinE polypeptide, cdv3 (divIVA) gene encoding a        Cdv3 (DivIVA) polypeptide, a FtsZ gene encoding a FtsZ        polypeptide, a Ftn2 gene encoding a Ftn2 polypeptide, or a        combination thereof.    -   22. The cyanobacterial population of statement 21, wherein the        mutant cyanobacterial cells comprise a MinC gene encoding a MinC        polypeptide that has reduced MinC activity, a MinD gene encoding        a MinD polypeptide that has reduced MinD activity, a MinE gene        encoding a MinE polypeptide that has reduced MinE activity, a        cdv3 gene encoding a Cdv3 polypeptide that has reduced Cdv3        activity, or a Ftn2 gene encoding a Ftn2 polypeptide has reduced        Ftn2 activity or a FtsZ gene encoding a FtsZ polypeptide has        reduced FtsZ activity.    -   23. The cyanobacterial population of statement 21 or 22, where        the reduced MinC protein activity, reduced MinD protein        activity, reduced MinE protein activity, reduced Cdv3 (DivIVA)        protein activity, reduced Ftn2 activity, or reduced FtsZ        activity is measured by less FtsZ polymerization than wild type        cyanobacterial MinC protein activity, MinD protein activity,        MinE protein activity, Cdv3 (DivIVA) protein activity, Ftn2        protein activity, or FtsZ protein activity of the same species.    -   24. The cyanobacterial population of any of statements 21-23,        wherein the mutant cyanobacterial cells comprise a MinC gene        encoding a MinC polypeptide that has less than 99%, or less than        98%, or less than 95%, or less than 90%, or less than 85%, or        less than 75%, or less than 60%, or less than 50%, or less than        40%, or less than 30%, or less than 20% sequence identity to any        of SEQ ID NOs:4, 6-9, or 10.    -   25. The cyanobacterial population of any of statements 21-24,        wherein the mutant cyanobacterial cells comprise a MinD gene        encoding a MinD polypeptide that has less than 99%, or less than        98%, or less than 95%, or less than 90%, or less than 85%, or        less than 75%, or less than 60%, or less than 50%, or less than        40%, or less than 30%, or less than 20% sequence identity to any        of SEQ ID NOs:14, 16-18, or 19.    -   26. The cyanobacterial population of any of statements 21-25,        wherein the mutant cyanobacterial cells comprise a MinE gene        encoding a MinE polypeptide that has less than 99%, or less than        98%, or less than 95%, or less than 90%, or less than 85%, or        less than 75%, or less than 60%, or less than 50%, or less than        40%, or less than 30%, or less than 20% sequence identity to any        of SEQ ID NOs:23, 25-31, or 32.    -   27. The cyanobacterial population of any of statements 21-26,        wherein the mutant cyanobacterial cells comprise a cdv3 (divIVA)        gene encoding a Cdv3 (DivIVA) polypeptide that has less than        99%, or less than 98%, or less than 95%, or less than 90%, or        less than 85%, or less than 75%, or less than 60%, or less than        50%, or less than 40%, or less than 30%, or less than 20%        sequence identity to any of SEQ ID NOs:33, 35-38, or 39.    -   28. The cyanobacterial population of any of statements 21-27,        wherein the mutant cyanobacterial cells comprise a Ftn2 gene        encoding a Ftn2 polypeptide that has less than 99%, or less than        98%, or less than 95%, or less than 90%, or less than 85%, or        less than 75%, or less than 60%, or less than 50%, or less than        40%, or less than 30%, or less than 20% sequence identity to SEQ        ID NO:45.    -   29. The cyanobacterial population of any of statements 21-28,        wherein the mutant cyanobacterial cells comprise a FtsZ gene        encoding a FtsZ polypeptide that has less than 99%, or less than        98%, or less than 95%, or less than 90%, or less than 85%, or        less than 75%, or less than 60%, or less than 50%, or less than        40%, or less than 30%, or less than 20% sequence identity to any        of SEQ ID NOs:40, 42, or 44.    -   30. The cyanobacterial population of any of statements 21-29,        wherein the mutant cyanobacterial cells comprise a MinC, MinD,        MinE, cdv3 (divIVA), Ftn2, or FtsZ gene comprising mutations in        at least one conserved amino acid position, or at least two        conserved amino acid positions, or at least three conserved        amino acid positions, or at least five conserved amino acid        positions, or at least seven conserved amino acid positions, or        at least eight conserved amino acid positions, or at least ten        conserved amino acid positions, or at least fifteen amino acid        positions, or at least twenty conserved amino acid positions, or        at least twenty-five amino acid positions.    -   31. The cyanobacterial population of any of statements 21-30,        wherein the mutant cyanobacterial cells comprise a deletion or        mutation in a conserved domain of a MinC, MinD, MinE, cdv3        (divIVA), Ftn2, or FtsZ gene, or a deletion or mutation in a        combination of conserved domains in one or more of MinC, MinD,        MinE, cdv3 (divIVA), Ftn2, and FtsZ genes.    -   32. The cyanobacterial population of any of statements 20-31,        wherein the mutant cyanobacterial cells comprise a deletion or        mutation in a MinC, MinD, MinE, cdv3 (divIVA), Ftn2, or FtsZ        gene, or a combination of mutations or deletions in one or more        MinC, MinD, MinE, cdv3 (divIVA), Ftn2, and FtsZ genes.    -   33. The cyanobacterial population of any of statements 21-32,        wherein the mutant cyanobacterial cells comprise a deletion of        an entire endogenous MinC, MinD, MinE, cdv3 (divIVA), or Ftn2        gene, or a combination MinC, MinD, MinE, cdv3 (divIVA), and Ftn2        genes.    -   34. The cyanobacterial population of any of statements 21-33,        wherein the mutant cyanobacterial cells comprise a MinC gene or        a MinD gene with a mutation of an operably linked MinCD        promoter.    -   35. The cyanobacterial population of any of statements 21-34,        wherein the mutant cyanobacterial cells comprise a MinC gene or        a MinD gene with a deletion, insertion, or modification of an        operably linked endogenous MinCD promoter.    -   36. The cyanobacterial population of any of statements 21-35,        wherein the mutant cyanobacterial cells comprise a MinC gene or        a MinD gene with a mutation of an operably linked endogenous        MinCD promoter, where the mutant promoter has less than 99%, or        less than 98%, or less than 95%, or less than 90%, or less than        85%, or less than 75%, or less than 60%, or less than 50%, or        less than 40%, or less than 30%, or less than 20% sequence        identity to SEQ ID NO:11 and/or 20.    -   37. The cyanobacterial population of any of statements 21-36,        wherein the mutant cyanobacterial cells comprise a MinC gene,        MinD gene, MinE gene, cdv3 (divIVA) gene, Ftn2 gene, or FtsZ        gene with a deletion of at least one nucleotide of an operably        linked endogenous promoter.    -   38. The cyanobacterial population of any of statements 21-37,        with a mean cell length that is at least 10% smaller than a wild        type population of cyanobacteria of the same species.    -   39. The cyanobacterial population of any of statements 21-38,        with a mean cell length that is at least 15%, or at least 20%,        or at least 25%, or at least 30%, or at least 35%, or at least        40%, or at least 45%, or at least 50% less than the mean cell        length of a wild type population of cyanobacteria of the same        species.    -   40. The cyanobacterial population of any of statements 21-39,        with a mean cell length that is at least 150%, or at least 200%,        or at least 250%, or at least 300%, or at least 500%, or at        least 750%, or at least 1000%, or at least 5000%, or at least        10000%, or at least 15000%, or at least 20000% greater than a        wild type population of cyanobacteria of the same species.    -   41. A targeting vector comprising two flanking segment, a first        targeting segment that has at least 70%, or at least 75%, or at        least 80%, or at least 85%, or at least 90%, or at least 95%, or        at least 97%, or at least 98%, or at least 99% sequence identity        to SEQ ID NO:12 and a second targeting segment that has at least        70%, or at least 75%, or at least 80%, or at least 85%, or at        least 90%, or at least 95%, or at least 97%, or at least 98%, or        at least 99% sequence identity to SEQ ID NO:13.    -   42. A targeting vector comprising two flanking segment, a first        targeting segment that has at least 70%, or at least 75%, or at        least 80%, or at least 85%, or at least 90%, or at least 95%, or        at least 97%, or at least 98%, or at least 99% sequence identity        to SEQ ID NO:21 and a second targeting segment that has at least        70%, or at least 75%, or at least 80%, or at least 85%, or at        least 90%, or at least 95%, or at least 97%, or at least 98%, or        at least 99% sequence identity to SEQ ID NO:22.    -   43. A method comprising (a) expressing a MinC, MinD, MinE, Cdv3        (DivIVA), FtsZ, or Ftn2 protein from a heterologous promoter, or        a combination of two or more MinC, MinD, MinE, Cdv3 (DivIVA),        FtsZ, or Ftn2 proteins from one or more heterologous promoter(s)        in a cyanobacteria to generate a transformed cyanobacteria;        and (b) establishing a cyanobacterial population comprising the        transformed cyanobacteria.    -   44. The method of any statement 43, wherein each promoter is a        constitutive promoter, inducible promoter, regulated promoter,        cell specific promoter, or synthetic promoter.    -   45. The method of any statement 43 or 44, wherein one or more        promoter is active before or during log phase growth of the        cells in a culture or fermentation medium.    -   46. The method of any of statements 43-45, wherein the promoter        is active at the end, or after, log phase growth of the cells in        a culture or fermentation medium.    -   47. The method of any of statements 43-46, wherein the        cyanobacterial population has a mean cell length of at least 10%        larger than a wild type population of cyanobacteria of the same        species.    -   48. The method of any of statements 43-47, where the population        has a mean cell length that is at least 150%, or at least 200%,        or at least 250%, or at least 300%, or at least 500%, or at        least 750%, or at least 1000%, or at least 5000%, or at least        10000%, or at least 15000%, or at least 20000% greater than a        wild type population of cyanobacteria of the same species.    -   49. The method of any of statements 43-48, where the population        has a mean cell length that is at least 10% smaller than a wild        type population of cyanobacteria of the same species.    -   50. The method of any of statements 43-46 or 49, where the        population has a mean cell length that is at least 15%, or at        least 20%, or at least 25%, or at least 30%, or at least 35%, or        at least 40%, or at least 45%, or at least 50% less than the        mean cell length of a wild type population of cyanobacteria of        the same species.    -   51. A method comprising (a) deleting or mutating a genomic MinC        site, a genomic MinD site, a genomic MinE site, a genomic cdv3        (divIVA) site, a genomic Ftn2 site, or a combination of one or        more genomic MinC site, genomic MinD site, genomic MinE site,        genomic cdv3 (divIVA) site, genomic Ftn2 site(s) in a        cyanobacteria to generate a mutant cyanobacteria; (b)        establishing a cyanobacterial population comprising the mutant        cyanobacteria, wherein the cyanobacterial population has a mean        cell length of at least 10% smaller than a wild type population        of cyanobacteria of the same species.    -   52. A method comprising expressing a MinC, MinD, MinE, Cdv3        (DivIVA), FtsZ, or Ftn2 protein from a heterologous promoter, or        a combination of two or more MinC, MinD, MinE, Cdv3 (DivIVA),        FtsZ, or Ftn2 proteins from one or more heterologous promoter(s)        in a cyanobacteria.    -   53. The method of statement 52, wherein the cyanobacteria is a        population of cyanobacteria in culture medium or fermentation        medium.    -   54. The method of statement 52 or 53, wherein each promoter is a        constitutive promoter, inducible promoter, regulated promoter,        cell specific promoter, or synthetic promoter.    -   55. The method of any of statements 52-54, wherein the promoter        is active before or during log phase growth of the cells in a        culture or fermentation medium.    -   56. The method of any of statements 52-55, wherein the promoter        is active at the end, or after, log phase growth of the cells in        a culture or fermentation medium.    -   57. The method of any of statements 52-55, wherein the        cyanobacteria also produces an oil (e.g., one or more fatty        acids), alkene, polyhydroxybutyrate, biomass, carbohydrate,        phycocyanin, ethanol, hydrogen, isobutanol, ethylene, or a        combination thereof.    -   58. The method of any of statements 52-57, further comprising        harvesting the cyanobacteria.    -   59. The method of any of statements 52-58, further comprising        isolating an oil (e.g., one or more fatty acids), alkene,        polyhydroxybutyrate, biomass, carbohydrate, phycocyanin,        ethanol, hydrogen, isobutanol, ethylene, or a combination        thereof from the cyanobacteria.    -   60. The method of any of statements 52-59, where a native gene        encoding a MinC, MinD, MinE, Cdv3 (DivIVA), FtsZ, or Ftn2        protein, or a combination of two or more native genes encoding a        MinC, MinD, MinE, Cdv3 (DivIVA), FtsZ, or Ftn2 protein, in the        cyanobacteria are mutated or deleted so that expression of the        MinC, MinD, MinE, Cdv3 (DivIVA), FtsZ, and/or Ftn2 protein in        the cyanobacteria is from the heterologous promoter.

The specific methods and compositions described herein arerepresentative of preferred embodiments and are exemplary and notintended as limitations on the scope of the invention. Other objects,aspects, and embodiments will occur to those skilled in the art uponconsideration of this specification, and are encompassed within thespirit of the invention as defined by the scope of the claims. It willbe readily apparent to one skilled in the art that varying substitutionsand modifications may be made to the invention disclosed herein withoutdeparting from the scope and spirit of the invention. The inventionillustratively described herein suitably may be practiced in the absenceof any element or elements, or limitation or limitations, which is notspecifically disclosed herein as essential.

The methods and processes illustratively described herein suitably maybe practiced in differing orders of steps, and the methods and processesare not necessarily restricted to the orders of steps indicated hereinor in the claims. As used herein and in the appended claims, thesingular forms “a,” “an,” and “the” include plural reference unless thecontext clearly dictates otherwise. Thus, for example, a reference to “anucleic acid” or “a promoter” includes a plurality of such nucleic acidsor promoters (for example, a solution of nucleic acids or a series ofpromoters), and so forth. Under no circumstances may the patent beinterpreted to be limited to the specific examples or embodiments ormethods specifically disclosed herein. Under no circumstances may thepatent be interpreted to be limited by any statement made by anyExaminer or any other official or employee of the Patent and TrademarkOffice unless such statement is specifically and without qualificationor reservation expressly adopted in a responsive writing by Applicants.

The terms and expressions that have been employed are used as terms ofdescription and not of limitation, and there is no intent in the use ofsuch terms and expressions to exclude any equivalent of the featuresshown and described or portions thereof, but it is recognized thatvarious modifications are possible within the scope of the invention asclaimed. Thus, it will be understood that although the present inventionhas been specifically disclosed by preferred embodiments and optionalfeatures, modification and variation of the concepts herein disclosedmay be resorted to by those skilled in the art, and that suchmodifications and variations are considered to be within the scope ofthis invention as defined by the appended claims and statements of theinvention.

What is claimed:
 1. A cyanobacterial population comprising cells with atleast one expression cassette comprising a heterologous promoteroperably linked to a nucleic acid segment encoding a Cdv3 protein with asequence comprising at least 95% sequence identity to SEQ ID NO:33. 2.The cyanobacterial population of claim 1, wherein the promoter is aconstitutive promoter, inducible promoter, regulated promoter, cellspecific promoter, or synthetic promoter.
 3. The cyanobacterialpopulation of claim 1, wherein the promoter is active before or duringlog phase growth of the cells in a culture or fermentation medium. 4.The cyanobacterial population of claim 1, wherein the promoter is activeat the end, or after, log phase growth of the cells in a culture orfermentation medium.
 5. The cyanobacterial population of claim 1,wherein the promoter is not a native promoter that would express theCdv3 protein in a wild type cyanobacteria.
 6. The cyanobacterialpopulation of claim 1, with a mean cell length that is at least 150%greater than a mean cell length of a wild type population ofcyanobacteria of the same species.